Eagle Bolt & Supply 5444 S 103rd E Ave, Tulsa, OK 74146 918-627-1123


​Hex nuts come in a vast array of types, materials, and specific functions for every industry and application one could possibly think of. Hex nuts are one of the most common nuts available and are used with anchors, bolts, screws, studs, threaded rods and on any other fastener that has machine screw threads. Hex is short for hexagon, which means they have six sides. Hex nuts are also known as: finished hex nuts, hex full nuts. Lock washers may be used with hex nuts.
Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine). Left-hand threaded hex nuts are also available—see Left Hand Nuts.

Hex nut size refers to its nominal thread diameter. Typically, sizes range from 1/4″ to about 2 1/2″. Size is specified in inches, usually fractional rather than decimal. Table 1 lists width across flats and across corners, and thickness.

Width across flats, which is wrench size, ranges from 1.50 to 1.75 times the nominal hex nut size and thickness is 0.850 to 0.875 times the size. Nuts that are 5/8″ and smaller are double (top and bottom) chamfered (beveled); larger sizes may be double chamfered or have a washer face bearing (bottom) surface and a chamfered top.

To ensure full thread engagement with the hex nut, bolts/screws should be long enough to allow at least two full threads to extend beyond the nut face after tightening. Conversely, there should be two full threads exposed on the head side of the nut to make sure the nut can be properly tightened.

Unlike materials such as stainless steel and brass, steel hex nuts are available in different strength “grades” as designated by the SAE (Society of Automotive Engineers). Grade 2 is the lowest, in terms of both strength and cost; Grade 5 offers medium strength; and Grade 8 is the highest SAE grade and is usually priced the highest as well. Never replace a graded hex nut with a lower grade or lower strength nut. Surface markings identify the grade.

Common materials include steel (unplated and plated—see more about finishes below), stainless steel, brass, silicon bronze, aluminum and nylon. Steel remains the least costly material followed by stainless steel; copper alloys (such as brass and silicon bronze) are the most expensive.

Common finishes for steel are zinc plating and hot dip galvanizing. Zinc, the most popular and least expensive commercial plating, offers moderate corrosion resistance. Hot dip galvanized is a thick coating of zinc that protects against corrosion in harsh environments. Stainless steel, though, is a better choice when corrosion is of concern except when submerged in salt water without free oxygen where it can suffer from severe pitting corrosion. Unplated and uncoated steel hex nuts—referred to as plain finish—may also be available and are susceptible to rust. Not all types are available in all materials and finishes.

Always follow the manufacturer’s recommendations regarding nut reuse, thread lubricants/locking compounds and torque values. It is advisable to match materials and finishes of hex nuts, washers and bolts/screws. When using hot dipped galvanized bolts, always use hot dipped galvanized nuts, which are tapped oversize (threaded larger than normal) to accommodate the thick zinc coating on the bolts (using a galvanized nut on a non-galvanized bolt will result in an unacceptably loose fit and using a plain finish or zinc plated nut on a hot dip galvanized bolt will result in a fit that is much too tight).

Stainless steel hex nuts and bolts/screws used together are susceptible to thread galling and seizing. While it may not be completely preventable, it can be substantially reduced. A thread lubricant is the most effective method. Alternatively, stainless steel alloys having different hardnesses—like a 316 nut and a 304 bolt—have less tendency to gall.

If you need a thinner nut, choose a jam nut. For smaller sizes—diameter, width and thickness—look at machine screw nuts. For a wider and thicker nut, consider a heavy hex nut.

In addition to the most standard nuts mentioned above, here is a list of many other types of nuts that are available: Machine screw nuts, Finished Hex nuts grade 2, 5, 8, Heavy Hex Nuts(Grade A, Grade C, Grade 2H, Grade DH, Grade DH3, Stainless Heavy Hex), Hex Jam Nut(Steel, Stainless Steel), Flange Nuts, K-Lock nuts, Serrated Flange Nuts, Automation Style Lock Nuts, Two Way Reversible Lock Nuts, Hex Cap Nuts(One piece, two piece, open ended), Nylon Insert Lock nuts(Standard pattern, Thin pattern, Heavy Hex, Heavy Hex thin), Hex Coupling Nuts, Flexloc Nuts(Light Hex Full Height, Light Hex Thin Height, Heavy Hex Full Height, Heavy Hex Thin Height), Slotted Hex Nuts, Hex Castle Nuts, Hex Panel Nuts, Tee Nuts, Wing Nuts, Square Nuts, and Spring Nuts. Some of the most popular and widely used types of nuts are lock nuts. Lock nuts come in many variations and styles. Each style is designed with specific locking features that lends itself to particular applications. Here’s a brief description of some of the most popular lock nuts.


Nylon insert lock nuts

A Nyloc (nylon insert) Nut is a torque prevailing nut which uses a plastic/nylon insert located towards the top of the nut, reducing its inner diameter, which then deforms over the mating thread. This captures the bolt or screw, providing a locking feature causing resistance or prevailing torque – keeping the nut locked in position and resistant to vibration. This design feature means that the screw threads do not cause damage to the plastic/nylon section allowing the nut to be re-used – although the locking feature will deteriorate after persistent re-use.

The Nyloc nut is an economic locking nut and ideal in applications where vibration or motion could loosen or undo the nut.

The nut can also be used to assist sealing the bolt thread against seepage of oil, water, petrol, paraffin and other liquids. They can be used in environments with relatively high temperatures where they can retain their locking ability up to 121°C.


Unitorque Nuts

All-metal prevailing torque hex nuts with a conical top and a flat bottom bearing surface with chamfered corners. The locking action, created by distortion of their top threads, is said to be capable of withstanding severe vibration and shock loads. Since they are top locking and only the bottom surface is flat, Unitorque lock nuts are considered one way lock nuts because they are installed one way—top up. Being all-metal, they are not subject to the temperature and chemical limitations of non-metallic (such as nylon) insert type lock nuts. Used in the automotive, agricultural equipment and metalworking industries, their cone shape allows for proper orientation during automated assembly making them popular for high volume applications. Unitorque lock nuts are also called: automation lock nuts, Auto Lock nuts, Crown Lock nuts, Stover lock nuts. Lock washers are not used with prevailing torque lock nuts.

By definition, “Prevailing-torque locking fasteners have a self-contained feature which creates frictional interference between the threads of the mating components.” Consequently, unlike free spinning lock nuts, there is a resistance to rotation during both assembly and disassembly requiring them to be wrenched; that resistance is called prevailing torque.
The advantage is that disassembly is unlikely even if preload diminishes completely because of the remaining rotational resistance. Despite the fact they are called “lock nuts,” Unitorque lock nuts are not permanently locked in place so they can be adjusted or removed after installation. And because they stay put without being seated, they are used as stop nuts or spacers for rotating or other components.
Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine).


K-lock nuts

Keps nuts are hex nuts with captive (non-removable) free-spinning lock washers, which are often external tooth. The nut turns freely during installation until the lock washer contacts and bites into the mating surface as the nut is tightened. If the mating surface is painted or plated, corrosion can occur if the lock washer penetrates and removes the surface treatment. Used in commercial and industrial applications, Keps nuts are also known as: captive washer lock nuts, Keps lock nuts, K-Lock nuts. Since they are not prevailing torque type lock nuts, they are not “locked” until fully seated and tightened.

Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine).

Keps nut size refers to its nominal thread diameter. Typically, sizes range from about #4 to 3/8″. Sizes less than 1/4″ are listed as a number size (the larger the number the larger the size) while sizes that are 1/4″ and larger are specified in inches, usually fractional rather than decimal.

Nut width across flats, which is wrench size, and thickness vary with the size of the Keps nut.

Steel, zinc plated, is a common material and finish.

Keps nuts are popular because they are low cost, reusable and the one-piece solution saves time over installing a separate lock washer and nut. However, if either the nut or washer is damaged, both must be replaced. Since they are not prevailing torque type lock nuts, they are suitable for use on long threaded assemblies and will not gall mating threads.