What are the Different Types of Fastener Nuts?

Find the right hardware nut for your fastening job—from the simple hex nut to unique nuts with specific functions, such as the tamper-proof tri-groove nut.

Nuts are a basic piece of hardware that, when coupled with a compatible bolt, provide secure fastening in a variety of applications. With the wide array of different nuts available, determining exactly which nut to use for an application can sometimes be tough. This guide will review a broad range of nuts and some applications in which they're most commonly used.

Hex Finish Nuts

Hex Finish Nuts are used for fastening to a hex cap screw, socket cap screw, or bolt. As the name indicates, these nuts are hex shaped with internal threads and are fastened by using a wrench.

Heavy Hex Nuts

Same as a hex finish nut but thicker, larger, and heavier.

Hex Jam Nuts

Hex Jam Nuts are frequently used as a locknut, where it is "jammed" up against a standard nut to lock the two in place. It is also used when a nut needs to be locked in place without clamping to another object. Hex jam nuts are a low profile nut, usually half as tall as a standard nut.

Hex Machine Nuts

These are smaller than a hex jam or hex finish nut and are used with machine screws less than 1/4" diameter.

Structural Heavy Hex Nuts

Similar to hex finish nuts, structural heavy hex nuts are thicker and much stronger. They're used in steel-to-steel structural connections.

Flange Serrated Nuts

These nuts feature a wide flange which acts as an integrated washer. The serrated flange does not spin or move and is designed to evenly distribute the pressure of the nut over the part being secured. This creates a locking action which prevents the flange nut from loosening.

Keps-K Lock Nuts

Designed to make parts assembly more quick and convenient, Keps-K lock nuts have an attached free-spinning lock washer. They're also commonly identified as a Keps nut, a K-nut or a washer nut.

Nylon Hex Jam Nuts

Featuring a low profile, these nuts are internally threaded with a nylon insert designed to prevent loosening from vibration. Additionally, internal cross threads stop the nut from backing off the fastener.

Nylon Insert Lock Nuts

Similar to nylon hex jam nuts but with a taller profile.

Prevailing Torque Lock Nuts

These nuts feature chamfered corners and a conical top. This distortion in the top threads is designed to resist loosening from vibration. Commonly known as Stover nuts or one-way nuts since they are installed only one way—conical top up—they are often used in high-temperature applications.

Cap Nuts

Also known as an acorn cap nut, this nut is named for its shape. The domed top of the nut is designed to prevent contact with the external thread.

Wing Nuts

With wings on opposite sides of the body, wing nuts allow for manual turning and installation. Frequently used where the nut needs to be removed and retightened often.

Castle Nuts

A nut with slots cut into the top, castle nuts are for use with cotter pins to prevent loosening They're often used for low-torque applications such as holding a wheel bearing in place.

Slotted Hex Nuts

Similar to castle nuts, slotted hex nuts are also designed to be used with cotter pins to create a locking mechanism. They feature a lower hex profile than castle nuts which can make them a better option where space may be an issue for your application.

Knurled Thumb Nuts

These nuts feature a knurled outer surface instead of a hex design. This allows for tightening the nut by hand. They're frequently used in decorative finishes or applications.

Coupling Nuts

This elongated, threaded, hex-shaped fastener is used for joining two male threads, most frequently a threaded rod. The hex shape allows for tightening or loosening with a wrench.

Square Nuts

Frequently matched with square-head bolts, these four-sided nuts are available with either a flat or beveled top. Square nuts provide a greater surface contact area, making them more resistant to loosening.

Tri-Groove Nuts

These specialty nuts are installed using a unique Tri-Groove socket designed to grip the indentations along the outside of the fastener. This allows for the nut to be turned along the threads. They're commonly used with driver-less fasteners such as concrete anchors and carriage bolts to ensure a tamper-proof, secure assembly.


These nuts are frequently used to fasten wood, composite, or particle board with the top surface countersunk to leave a flat, flush surface. T-nuts feature 3 or 4 prongs which sink into the material surface for more secure fastening.

Break Away or Shear Nuts

Shear nuts are conical-shaped nuts with a hexagonal gripping point. They are designed with an intentional flaw to allow for the hex head to snap off once the maximum torque is reached. This leaves behind a protective cone nut that is tamper-resistant and can't be easily removed since there is now nothing remaining to grip.


Along with a wide array of hardware nuts, Zoro also supplies the tools you need to secure them in place. From ratcheting wrenches to adjustable wrenches and more, Zoro is sure to have just the right wrench to help finish any job.

Product Compliance and Suitability

The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.

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