Black oxide hex bolts

Different coating chemistries have long been used by fastener manufacturers to improve corrosion resistance, lubricity, or both. Understanding a solar fastener’s coating can ensure joint integrity, improve field life, and increase serviceability. 

Black oxide is a conversion coating used on fasteners made from ferrous (iron-containing) materials, copper and copper based alloys, stainless steel, zinc and more.Black oxide is sometimes used for appearance, to minimize the reflection of light, or for mild corrosion resistance. For black oxide to achieve maximum corrosion resistance properties, it must be impregnated with wax or oil. One advantage black oxide has over other coatings is its minimal buildup. Solar assemblies commonly use black oxide to coat a stainless steel fasteners for aesthetic purposes, creating an evenly colored black finish without compromising the integrity of the fastener. 

Inorganic coatings encompass anodizing, surface conversion, enameling, metallic coatings and more. Created through a chemical action that changes the surface layer of the metal into a metallic oxide film or compound, inorganic coatings are primarily used to reduce corrosion.

DURA-CON salt spray test results

In addition to the previously mentioned unbranded coatings, the Magni organization offers a selection of proprietary coatings for solar fasteners. The 565 coating from Magni allows lubricants to be integrated into the topcoat, which will typically eliminate the need for messy and cumbersome post-treatments. This non-electrolytically applied, zinc-and-aluminum-rich coating also eliminates the concern of hydrogen embrittlement. Able to be formulated in many colors, the Magni 565 coating also comes in several friction levels while still providing consistency across different bearing surfaces.

DURA-CON brand fasteners offer a variety of Grade 5 and standard steel fasteners that are coated to be suitable for use as solar fasteners. DURA-CON fasteners employ a three layer coating system consisting of an inorganic zinc-rich first coat and an aluminum-rich organic second coat. Friction modifiers are integrated into the topcoat, resulting in repeatable torque tension characteristics during assembly. Grade 5 bolts are stronger than A307 zinc, hot dip galvanized or 300 series stainless steel bolts, and DURA-CON coating provides superior corrosion resistance; easily withstanding 1500 hours of Salt Spray per ASTM B-117 with no corrosion whatsoever.

For more information about which coating type my be best for your solar fastener application, contact us today.

Though a particular solar application may call for a specific, less-common material, the majority of solar installation hardware is made up of one or a combination of four standard materials: 18/8 stainless steel, 316 grade stainless steel, 410 grade stainless steel, or Grade 5 steel.

Stainless Steel 18/8
The most widely used and flexible austenitic form of stainless steel, 18/8 stainless steel is 304 grade stainless steel. The numbers 18/8 are a representation of what makes up the material; 18% chromium and 8% nickel. This chemical makeup creates a material that is very resistant to both oxidation and corrosion. 18/8 stainless steel is common for sheet metal screws and most nuts used in solar installations.

Stainless Steel 316
Known for its 2-3% molybdenum content, 316 grade stainless steel is an austenitic form of stainless steel. The additional molybdenum creates a metal that is more resistant to pitting and corrosion, and it also improves resistance to failure caused by very high temperatures. Particularly effective when used in acidic environments, corrosion that is caused by acetic, hydrochloric and other forms of acids can be prevented by using fasteners made from 316 stainless, but the metal is softer than 18/8 stainless or 410 stainless.

Stainless Steel 410
Containing 11.5% chromium, 410 grade stainless steel is general-purpose martensitic stainless, providing reliable corrosion resistance in most cases. Additionally, the corrosion resistance of 410 grade stainless can be further enhanced by processes like tempering, hardening and polishing. Fasteners made from 410 stainless are generally used for applications involving the need for mild corrosion resistance, high heat resistance and high strength performance. Self-drilling screws used in solar applications are commonly made from 410 grade stainless steel.

Grade 5 Steel
Grade 5 is a zinc-plated, medium carbon alloy steel that has been heat treated to increase its hardness. Bolts made from Grade 5 steel are identified by three evenly spaced hash marks on the bolt’s head, and sometimes a manufacturers mark or logo may also be included. During the manufacturing of Grade 5 cap screws, the screws are heated to strengthen the outside, creating a stronger outside than inside of the fastener. When Grade 5 steel is used in a solar application, it is typically coated in a very corrosion resistant finish.

Bi-Metal Fasteners
A bi-metal screw, as the name suggests, is a. screw comprised of two metal types. The point is typically made from a high carbon steel that has been heat treated, giving it the ability to self-drill. The body is then made from stainless steel so as to provide the resistance to corrosion. One example of a highly popular bi-metal fastener is the Elco Bi-Flex structural screw, which are self-drilling, self-tapping screws that provide the efficiency of drill screws combined with the corrosion resistance of 300 series stainless steel. Bi-Flex screws can be used in both steel and aluminum racking.

If you want to know more about which material the fasteners for your particular solar assembly should be made of, contact China Special Fasteners for assistance.

For bolted connections in any outdoor environment, avoiding corrosion is going to be key to preserving the integrity of the assembly. This is of course true for fasteners used in solar installations, since they’re not only exclusively used in outdoor environments, but often in some with the harshest exposure to the elements.

Joints exposed to a corrosion attack suffer deterioration. Failure caused by corrosion should receive priority attention, but even small amounts of corrosion causing loss of material can result in loss of preload.

To reduce the possibility of corrosion in bolted connections, consider the following:

• Use corrosion resistant and compatible materials.

• Basic factors affecting how a corrosion-resistant fastener should be chosen:

  • tensile strength

  • fatigue strength

  • position of the fastener and materials to be joined on the galvanic series scale

• Basic factors affecting how a corrosion resistant protective coating for fasteners should be chosen:

  • Level of corrosion resistance

  • Limitations due to temperature

  • Base metal embrittlement

  • Any effect the coating may have on fatigue life

  • Any effect the coating may have on locking torque

  • Whether or not the coasting is compatible with adjacent material

  • If the coating will cause any dimensional changes

  • Thickness & distribution

  • Adhesion characteristics

• Protect from environmental exposure

Want to learn more about preventing corrosion in bolted connections? Contact us for assistance.

The third consideration for bolted connections in solar installations is the possibility of fatigue and its effects on the integrity of the assembly.

Dynamic and alternating service loads will cause a bolt to fracture at a load less than its static tensile strength. That Fatigue Strength is the maximum tensile load a material can support before fracturing prior to a given number of loading cycles. As load is reduced, the number of loading cycles that a bolt can endure increases until a level known as the Endurance Limit Δ is reached, at which a bolt will function with immunity against fatigue.

Here are some guidelines to preventing fatigue:

• High preloads protect bolts against failure.

• When the portion of the fluctuating service load is less than the bolt’s endurance limit, the fatigue life is essentially infinite.

If you’re looking for help preventing fatigue in bolted connections for your solar panel installation, contact China Special Fasteners to get the assistance you need.

Two fatigue cracks have developed. The central area is the last to fail. Examination of the threads confirmed the bolt was loose.

In addition to the threat of relaxation described previously, vibration is another way in which bolted connection in solar installations can be compromised.

In tightened fasteners, frictional resistance develops between the bolt and nut threads and between the bolt head and the nut against the joined material. If this resistance is reduced, even for a microsecond, tensile stress in the bolt will cause the mating threads to loosen. Locking mechanisms can be employed to resist loosening.

To prevent loosening caused by vibration, consider taking the following steps:

• The best way to clamp the joined material sufficiently that the frictional resistance exceeds any applied shear force that will occur in service. Properly preload the bolt.

• Adjusting joint geometry to provide a mechanical restraint.

• Use jam nuts, slotted nuts with a cotter pin.

• Use anaerobic adhesives to cement threads together.

• Use self-locking fasteners such as locknuts, nylon thread patches or pellets, or wedge-lock type washers.

If you have any questions about how to prevent loosening due to vibration in a solar fastener connection, don’t hesitate to contact us for additional help.

When considering bolted joints in solar installations, there are a few factors that may influence the connection’s integrity, one of which is relaxation.

All joints experience some relaxation after assembly with an accompanying loss of preload. Additional relaxation may occur during the service life of the joint depending on time, loading type and level, and environment. If a joint relaxes too much, loss of preload may result in joint separation and failure.

In order to combat relaxation of a bolted assembly in a solar installation, take the following precautions:

• Limit joint interfaces.

• Ensure smooth surfaces.

• Control parallelism of joint surfaces.

• Use flange head bolts and flange nuts to reduce bearing stresses against joint material.

• Use hardened washers under bolt head and nut to distribute bearing stresses.

• Use smaller diameter higher strength bolt to increase elasticity.

If you have questions about how to minimize the threat of relaxation in bolted joints, please contact us.

The term “solar fasteners” is used to describe any fasteners used to install a solar power system. Typically, solar fasteners are standard parts that are used in other industries besides solar. Sometimes a solar company will design a custom fastener specific to their system. Different types of fasteners may be required depending on the method of installation.

To start; a fastener is a piece of hardware that affixes two or more objects together. Solar power design uses two broad categories of fasteners: mobile fasteners and permanent fasteners.

Mobile fasteners are bolts, nuts, washers, and some screws. Those fasteners are designed to create a temporary union between two objects. This temporary union means you can remove these fasteners without causing damage to the assembly. Rivets, welds, lockbolts and some screws are considered permanent fasteners, designed to create a permanent assembly between two objects. This means that if you remove one of these fasteners, you’ll cause damage to the union. The correct fastener will be dictated by the design of the solar system.

Extreme environmental conditions are frequently present at the location of a solar power installations. Solar fasteners need to be durable enough to maintain the structural integrity of a PV (photovoltaic) system. Choosing the right fastener, in right material, with the right coating, will help ensure the longevity of the joint.

Washers can be plated or finished with a variety of coatings, ranging from the highly corrosion resistant DURA-CON coating to more simplistic metallic or painted finishes. Washers are sometimes coated for functional purposes, and sometimes for purely aesthetic reasons. Whatever the reason for using a particular coating or finish on a washer, we’re here to help to understand which would be best for your application. Let’s start with the three most common finished applied to washers.

Zinc / Trivalent Zinc

The most popular commercial platings, zinc is both economical and corrosion resistant, commonly used in environments where excessive moisture will not be present. On top of the zinc, a clear chromate finish is applied to create an additional layer of protection against white oxidation spots that can form in the presence of moisture. The most common way of applying zinc coatings to fasteners is through electroplating.

Black Oxide

Black oxide is a "conversion coating", meaning it is formed by a chemical reaction with the metal to form an integral surface, as opposed to an "applied coating" like zinc which bonds to the metal. A post-coating oil finish is typically applied to inhibit the development of rust.

Galvanized

Hot dip galvanizing can be highly effective as a method to apply a sufficient thickness of zinc for corrosion protection in particularly harsh environments. Steel reacts with molten zinc during the galvanizing process, which forms layers of zinc-iron alloy that are bonded metallurgically with the steel surface. The hard barrier created during this process not only resists mechanical damage, but also has a very low rate of corrosion.

If you have further questions about finishes for washers, please don’t hesitate to contact us for more information.

Certain applications require specialty washers that don’t necessarily fit into one of the earlier specified categories of flat washers, spring washers, lock washers and structural washers. Here we will look at three of the most common specialty washers used in industrial applications.

Tab Washers

Tab washers are a less common type of lock washer, featuring a tab that can be bent up against the flat of a bolt head or hex nut, thereby preventing rotation of both the washer and bolt or nut. The tabs on these types of washers can be internal or external, can have one tab or multiple tabs, and can be manufactured in large outer diameters of up to 12 inches.

Slotted Washers (C Washers)

Slotted washers feature a slot in the side that creates the appearance of the letter C and allows the user to install and remove the washer without completely disassembling the joint. Slotted washers can be used in a variety of ways, but are often used as shims or as a way to increase productivity in the process of repositioning an assembly.

Finishing Washers (Countersunk Washers)

Finishing washers, also known as countersunk washers, are used primarily for decorative appearance. A countersunk screw can be recessed into the finishing washer to create a flush, flat surface, therefore also creating a very clean appearance.

If you have further questions about specialty washers, please don’t hesitate to contact us for more information.

The term structural washer is generally inclusive of washers used in an assembly with structural bolts, or any assembly that is integrative to the structural integrity of an engineered joint.

Load Indicating Washers (Direct Tension Indicator Washers - DTI)

Load indicating washers were developed in the 1960s and contain raised protrusions that collapse as an assembly is tightened. To develop the correct tension, these washers should be used when installing A325 or A490 structural bolts. Both of the most common load indicating washer, standard DTIs and SquirterTM DTIs, are made to meet the specifications of ASTM F959.

Square Washers

Square washers look exactly as they, shaped like a square to fit into channels and slots. The flat sides prevent the washers from rotating in an assembly, and are thicker and wider than common round washers, helping to distribute heavy loads more evenly.

Cross Bracing Washers (Hillside Washers)

Cross bracing washers, also known as hillside washers, are used when connecting structural beams to cross-bracing rods or cables. These washers feature a curved top surface that allows rods to pass through and a nut to be secured at different angles, while the flat bottom side sits flush against structural beams. Cross bracing washers also contain a locking tab that make them stay in place when force is applied.

Malleable Washers

Malleable washers are cast iron round washers most commonly used in wood dock construction. The large bearing surface of these oversized washers prevents nuts and bolt heads from pulling into their wood substrate.

If you have further questions about structural washers, please don’t hesitate to contact us for more information.

Spring washers have flexibility that is utilized to prevent loosening during vibration. They are “sprung” in order to maintain a consistent preload on the adjacent fastener as the joint experiences movement.

Split Lock Washers (Helical Washers)

Split lock washers, or helical washers, looks like a ring with uneven ends. When tightened, these ends flatten to add tension to an assembly, thereby preventing the joint from loosening as a result of vibration. Split lock washers are used in a wide array of applications, but if your application is likely to experience extreme vibration, it might be better to consider a wedge washer or other type of lock washer.

Conical Washers (Dish Spring Washers)

Known by many different names, including conical spring washers, cupped spring washers, Belleville washers and more, conical washers create a very compact spring due to their shell-like shape. Conical washers are unique in their ability to be stacked, either in the same direction to create increased spring stiffness, or in the opposite direction to create increased range of motion.

Wave Washers

Wave washers have been pressed to create a wavy pattern, which acts as a spring when compressed with a threaded fastener. Due to their relative lightness, wave washers produce low preload forces.

If you have further questions about spring washers, please don’t hesitate to contact us for more information.

Apart from the variety of standard flat washers covered in our last article, the next most common type of washers are lock washers. Lock washers contain mechanisms that prevent bolts and nuts from loosening in the face of torque and vibration, thereby creating their namesake “lock” on the assembly.

Internal Tooth Lock Washers

Internal tooth lock washers feature a series of “teeth” extending inward that “bite” into the bearing surface. The teeth help prevent a bolt head or nut from loosening, but also aid in absorbing shock and vibration.

External Tooth Lock Washers (Star Washers)

External tooth lock washers, sometimes known as star washers, feature teeth on the outside of the washer ring that bite into the bolt or screw head. For these washers to work properly, they should be used with screws and bolts that have larger diameter heads, such as pan head and button head fasteners.

Internal / External Tooth Lock Washers

These types of washers are exactly what they sound like, a combination of internal teeth and external teeth, and are often used in electrical bonding. Internal / external tooth lock washers are helpful when trying to span elongated holes, but can also be used between adjustable pieces of an assembly to help maintain the position of the components after the original tightening.

Wedge Washers

Wedge washers, or beveled washers, have serrations on one bearing face and are used in a pairing. The serrated face of each washer is paired against the serrated face of the other in the pair, causing them to indent into the nut and stopping the possibility of rotation. Wedge lock washers are commonly used in construction equipment, railroad, automotive, solar and wind power applications.

If you have further questions about lock washers, please don’t hesitate to contact us for more information.

For the next installment of our Everything but the Bolt educational series, we’ll be digging into the various types of washers available for industrial uses. Some applications will only require a basic flat washer, while some applications will require a very specific type of washer, either for functionality or to adhere to certain code requirements.

The most common type of washer is a basic round flat washer, also known as a plain washer. Flat washers used in conjunction with bolts provide a smoother bearing surface on the underside of the bolt head or nut.

USS Flat Washers

USS flat washers were developed as a standard (the USS is the abbreviation for United States Standard) for basic engineering requirements in most industrial applications. The specifications of Outer Diameter (OD), Inner Diameter(ID) and Thickness (Th) are made to appeal to the widest use and highest stability, allowing users to create extreme tightness at the joint in which they are being used.

SAE Flat Washers

SAE flat washer specifications were developed specifically by the Society of Automotive Engineers to meet automotive manufacturing requirements in a broad sense. They typically have smaller outer diameters and less thickness than their USS counterparts. Although SAE washers are mostly used in automotive applications, they are also recommended for use any time the assembly includes Grade 5 or Grade 8 hex cap screws.

Fender Washers

Fender washers offer an outside diameter, and therefore bearing surface, that is much larger than that of USS flat washers. The large outside diameter design helps to better distribute applied forces when tightening an assembly. Fender washers are most commonly used in sheet metal, plumbing, automotive and electrical applications.

Thru Hardened Washers

Thru hardened washers provide additional strength and protection by going through a process of hardening or carburizing. While typically of a smaller size than standard USS washers, hardened washers are recommend for us with Grade 8 bolts, as well as other heat-treated fasteners.

ANSI Washers

ANSI washers are flat washers that meet standard provided by the American National Standards Institute (ANSI). Type A washers take into consideration both narrow and wide sizes, while Type B washers come in narrow, regular and wide sizes. Though the difference between the two types can be very minimal, the precise sizing can come in handy for applications where the washer dimensions are critical to an assembly’s functionality.

If you have further questions about flat washers or plain washers, please don’t hesitate to contact us for more information.

In our last installment of Know Your Nuts, we’re reviewing some of the less common but still very important specialty nuts available for niche uses. All specialty nuts have a particular use case in which they excel, whether they’re being used for security, to overcome an engineering hurdle, or for a specific industry. Below are examples of several specialty nuts that may be beneficial to you when designing your fastened connections.

Coupling Nuts

Coupling nuts are threaded fasteners for joining two male threads together, such as threaded rods, pipes and other parts, including those with different sized parts. Coupling nuts can also be used to extend rod assemblies to longer length from shorter components. When a right hand/left hand coupling nut is required, the part needed is known as a sleeve nut.

Cage Nuts

Cage nuts typically consist of a square nut encased in a spring steel cage with wings that can be used to compress and release the nuts. Also known as captive nuts or clip nuts, the most common use of cage nuts is in different types of equipment racks and mounting rails.

Castle Nuts

Castle nuts, or castellated nuts, have grooved heads that align with holes in a mated bolt, allowing a cotter pin to be inserted and therefore locking the nut in place. Installed like a traditional hex nut, the castle nut is commonly used in low torque applications as a simple to use, low-cost means of protection against loosening caused by vibration.

Weld Nuts

Weld nuts are a type of specialized nut engineered specifically for the purpose of being welded to another metal component. Weld nuts are helpful when a very high strength connection is needed in an application with limited space. Weld nuts come in a variety of shapes, including square, round, tabbed and flange. Since weld nuts need to be welded, they usually come uncoated, to be painted or finished later after the welding is completed.

Wheel Nuts

A wheel nut, more commonly known as a lug nut, serves the specific purpose of securing a wheel to a vehicle. Automobiles, trucks, and other large vehicles with rubber tires are the most typical applications for wheel nuts.

Rivet Nuts

Rivet nuts, also known as blind rivet nuts or rivnuts, are one-piece internally threaded and counterbored tubular rivets. Rivet nuts are a type of threaded inserts, and can be anchored entirely from one side. One form of rivets nuts are designed to bulge on the back side as a fastener is tightened, locking the assembly into place. Rivet nuts are most commonly used in applications where the substrate is too brittle or thin for regular hole tapping, especially in tubing for electronics, aerospace and more.

Self-Clinching Nuts

Self-clinching nuts, also called swage nuts, provide a great solution for design engineers when a strong reusable thread is needed for their application. Self-clinching nuts can fasten softer materials permanently by anchoring into the material, and are often used in sheet metal and cable railing assemblies.

Tri-Groove Nuts

Tri-Groove nuts belong to a family of specialty fasteners known as “security fasteners” or “tamper-proof fasteners” and are commonly used in public applications like parks, campgrounds and community centers. Tri-Groove nuts are installed using a unique socket designed to grip the indentations on the outer body of the nut, allowing it to be turned along the threads. It’s typical for these security fasteners to be used with driver-less fasteners, like carriage bolts and concrete anchors, ensuring a fully tamper-resistant assembly.

Break Away Nuts

Break away nuts, or shear nuts, are another type of security fasteners used in assemblies where tampering could be a concern. These conical-shaped nuts feature a hexagonal gripping point, and are designed to allow the hex head to snap off, or “break away”, once the maximum torque is reached. What remains is a protective cone nut that is tamper-proof and extremely difficult to remove since nothing remains to be gripped.

If you have further questions about specialty nuts, please don’t hesitate to contact us for more information.

Next up in our educational series called Know Your Nuts, we’re talking about different types of shaped nuts. The use of shaped nuts varies from type to type, but in general, they all share some aspect of their design with more common standard nuts, with an extra feature added to achieve a specific functionality. Below are four of the shaped nuts most commonly used in construction and industrial applications.

Cap Nuts

Cap nuts are traditional hex nuts with the addition of a smooth dome on one side. These are used in assemblies where protection of the bolt or threaded is important after assembly, either for performance or for safety. Cap nuts can also be used for purely aesthetic reasons, such as in automotive uses or in residential construction, where the end of a bolt could cause an unsightly distraction for the user.

Acorn Nuts

Acorn nuts are a type of cap nut, where the domed side is pointed with a higher crown. This creates greater internal depth, allowing the bolt or rod to be threaded further into the nut.

Square Nuts

As opposed to the traditional hex (hexagonal) nut with its six sides, square nuts only have four sides and look exactly as they sound, a perfect square. Square nuts are typically used where there is an inset or channel in the receiving surface, such as in furniture, railroad applications, or other metal assemblies. The larger surface area of square nuts allows them to more easily resist loosening.

Wing Nuts

Wing nuts feature a head with two “wings” across from each other, making the nut able to be tightened and loosened by hand. Sometimes referred to as a “butterfly nut”, these are mostly used for the purpose of temporary fastening, but can also be found in bicycles and musical instruments.

If you have further questions about shaped nuts, please don’t hesitate to contact us for more information.

In our next edition of Know Your Nuts, we’ll be looking at the two most common types of nuts for wood. These nuts are used in applications where a durable thread is needed but the substrate is too soft for repeated assembly and disassembly. A common commercial use for these products is in the ready-to-assemble furniture industry, where products are shipped flat and need to be assembled by the consumer.

Tee Nuts

Tee nuts feature a thin, long body with a T-shaped flange at one end. The flange, which has 3 or 4 prongs attached to it, digs into the substrate to be flush with the surface, leaving it completely flat. Tee nuts are often used to fasten particle board, composite materials or wood more securely.

Insert Nuts

Insert nuts, sometimes called hex drive inserts, create a threaded socket for a wooden substrate, functioning much like a wall anchor. After a hole is pre-drilled, insert nuts are put into the hole, either by screwing or hammering it in. No matter how the nut is inserted, the external, teeth-like protrusions bite into the wooden substrate, which prevents the nut both from turning and from pulling out.

If you have further questions about nuts or inserts for wooden assemblies, please don’t hesitate to contact us for more information.

For our third edition of Know Your Nuts, we’re going to review the two most common types of structural nuts. The category of “structural nuts” includes heavy hex nuts that meet ASTM A194 GR. 2H, ASTM A563 GR. C, and ASTM A563 GR. DH specifications.

Grade 2H Nuts

Grade 2H nuts are a type of heavy hex nuts that distribute loads over a larger area, due to their size being about ten percent taller and ten percent wider and taller than standard hex nuts. Because Grade 2H nuts are similar in strength to Grade 9 bolts - roughly 20% stronger than typical steel nuts - uses in heavy machinery are quite common, such as assemblies in earth-moving equipment.

Grade DH Nuts

Grade DH nuts are heavy hex nuts made from medium carbon steel that have been heat treated. Designed and recommended to secure F3125 A490 structural bolts in assemblies, these nuts are often marked by the letters “DH”, although they are not required to be marked unless specified by the purchaser.

If you have further questions about structural nuts, please don’t hesitate to contact us for more information.

In our next edition of Know Your Nuts, we’re going to review the different types of all metal lock nuts. Designed to develop a “prevailing torque” between the bolt threads and nuts threads, all metal lock nuts increase the resistance to rotation in an assembly. Unlike nylon insert lock nuts, these nuts are effective in higher temperature environments (withstanding temperatures up to 1,400 °F ), since they’re completely made of metal. Below is a summary of the most common all metal lock nuts available.

Flange Nuts

Flange nuts feature a wide flange at one end that acts like an integrated washer, distributing the torquing pressure placed the nut across the surface of the material it’s being secured to. Often including serrations on the underside of the flange, these nuts are regularly used in assembly lines where the speed of using a single fastener, as opposed to separate nuts and washers, can help increase productivity and overall output.

Keps Nuts

Keps nuts are similar looking to standard hex nuts, but also include an attached, free-spinning washer. The washer is sometimes called a k-lock or star washer. A trademark of ITW Shakeproof, the name Keps is a reference to the “kep” in ShaKEProof, with an “s” typically added because more than one is purchased at a time.

Stover Lock Nuts

Stover lock nuts are single-piece, prevailing torque hex nuts that feature a conical top, flat bottom bearing surface, and chamfered corners. In Stover lock nuts, the locking action is created by distortion of their top threads during torquing, and can withstand severe shock loads and vibration.

Two-Way Reversible Lock Nuts

In a two-way reversible lock nut, a standard hex nut is compressed with two or three indentations on the flat sides of the nut. These compressions can be circular or rectangular, but must be equal distances from each other. In order to create a controlled locking mechanism, the compressions slightly distort the center threads that lock when engaged with the mating bolt or screw. Designed for use with machine screws and low-carbon bolts, the two-way reversible lock nut allows for automatic assembly.

If you have further questions about all metal lock nuts, please don’t hesitate to contact us for more information.

In the first installment of our Everything but the Bolt educational series, we’re taking a look at all different types of nuts. While many applications only need a very basic nut, we’ll review the different types of nuts (both standard and specialty), and give you the information you need to make a decision about which nut is best for your application.

We’ll start with the most quintessential version of a nut on the market - common hex nuts. Below is a description of the different types of common hex nuts available.

Finished Hex Nuts

A finished hex nut is the most basic of nuts - the six-sided nut that almost everyone first pictures in their mind when they hear the word “nut” in an industrial context.  Hex is short for hexagon, referencing the six sides of the nut. These nuts feature internal threading and are commonly used with machine thread bolts and screws, in applications where no “locking” mechanism is required.

Hex Jam Nuts

Hex jam nuts are low profile - usually only about half as thick as a standard hex nut. Commonly used as a type of lock nut, the jam nut is "jammed" against a standard nut to lock the two in place. Jam nuts are also sometimes used in applications where a traditional, larger profile hex nut would not fit.

Machine Screw Nuts

Designed specifically to be used with machine screws, these hex nuts are much smaller sizes than full-size hex nuts and feature flat tops and chamfered corners. Threads can be coarse (UNC) or fine (UNF), and zinc plating is the most common type of finish applied to machine screw nuts.

Nylon Insert Lock Nuts

Nylon insert lock nuts are very similar to basic finished hex nuts, but feature a nylon insert lock to help secure the nut into place. When a nylon insert lock nut is installed onto a bolt or screw, the nylon insert wraps around the threads, protecting the connection from loosening due to vibration.

If you have further questions about common hex nuts, please don’t hesitate to contact us for more information.

Have you ever looked at the head of a bolt and wondered what the markings mean? Maybe there's a series of letters and numbers, maybe just a few lines.

The markings on the heads of bolts serve two different purposes:

1. The markings can indicate who manufactured the bolt. This will vary from manufacturer to manufacturer, but is usually one, two or three characters.

2. The markings can identify the standard to which the bolt was made. For instance, if a bolt head contains three radial lines, then it's a Grade 5 bolt. If it contains five radial lines, then the bolt is Grade 8. If the bolt is manufactured to a particular grade based on standards set by the American Society for Testing and Materials (ASTM), then the marking will show a combination of letters and numbers.

China Special Fasteners wants to help you decipher these head markings and when you'll need to know them. Download our bolt head markings chart to reference any time you need to figure out the grade of a bolt you're using or looking for. If you still have questions not addressed in the chart, don't hesitate to contact us for help.

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