Nuts Information


Nuts are a type of hardware fastener with a tapped inner diameter. They are used with a mating threaded bolt or rod to secure components. There are many sizes and varieties of nuts; each with a particular fastening purpose. Some nuts can be applied without tools, and others may have special designs to prevent the nut from loosening.


Nut Operation


Most nuts require a rotational force around the bolt threads for application, though some nuts may be push-press or clip-on. No matter its application method, nuts hold components through the same mechanical property: the friction of the bolt and nut threads against one another, which is comprised of a slight stretch of the bolt from the compression resistance of the components being fastened, and a slight elastic deformation of the parts held together.



Some nuts will employ a locking mechanism to maintain a nut's position against the substrate for dynamic loads and vibration. Plastic inserts, misshapen threads, pins, or lockwire can all be used to lock a nut in place; nuts utilizing one of these methods are known as locknuts. In some instances, nuts of the same type--exerting different degrees of torque--can be used to secure nuts in position. Lock washers are another option for maintaining a nut's place on a bolt. Adhesive thread lockers may be suitable as well.




Nuts are commonly made of metal, but other options are available.


  • Aluminum nuts are light, resistant to oxidation, thermal and electrical conducive, and easy to manufacture.
  • Brass nuts are strong, conductive, corrosion resistant, with low magnetic permeability.
  • Copper alloy nuts have good load capacity, wear resistance, and are suitable for dynamic loads.
  • Fiber-reinforced plastic nuts use industrial fabric reinforced urethanes. They are wear resistant.
  • Inconel®/Incoloy®metal nuts provide good strength and oxidation/carbonization resistance in high temperatures. They can be used in temperatures up to 1200° F.
  • Monel®nuts are made of a proprietary metal blend with resistance to chemicals and solutions.
  • Nylon nuts are made of a tough and resistant material. It has good pressure ratings.
  • Plastic nuts are inexpensive and corrosion resistant for light loads.
  • Polytetrafluoroethylene (PTFE) is an insoluble compound and PTFE nuts have durability and low friction.
  • Polyvinyl chloride (PVC) is inert and resistant to chemicals, and PVC nuts are flexible, smooth, and non-toxic.
  • Polyvinylidene fluoride (PVDF) nuts has less creep and better strength than other fluoropolymers, but is susceptible at high temperatures.
  • Rubber nuts are used in specialty applications requiring vibration and noise dampening.
  • Steel nuts are produced of strong, carbonated iron. Uncoated steel is vulnerable to corrosion.
  • Hardened steel relies on hardening methods to produce a stronger, but more brittle, version of steel.
  • Stainless steel nuts are chemical and corrosion resistant with an appealing finish. They cannot be hardened like carbon steel.

  • Titanium nuts are hard and strong, light, and corrosion resistant. When alloyed with other metals, it increases strength and durability.

Production Units


Manufacturers produce nuts in both imperial and metric units, and due to their explicit correspondence with bolts and studs, the units cannot be mixed. Furthermore, nuts are produced with fine or coarse threads which is a designation of the nut's thread pitch--not the quality of the product. Coarse-thread nuts are less susceptible to galling, thread crossing, and seizing, while fine-thread nuts are less likely to loosen from jostling, and are more easily tapped and adjusted.




For imperial sizes, nut producers will provide a designated number or fractional inch for the dimension of the nut. North American countries follow this system, called the Unified Thread Standard. Also included will be a "threads per inch" (TPI) count which will indicate a course or fine thread. 



Additionally, nuts are sometimes given a tolerance class, which indicates their precision in an assembly. Class 1B threads are loose fitting for easy assembly and dirty arenas. Class 2B is the most common thread class, and is designed for maximum strength with common precision. Class 3B provides the least assembly tolerance.




Metric units are designated by the ISO 261: metric screw thread; it is the most common screw thread in the world. These nuts will have diameters and thread pitches in millimeters



There are five possible tolerances for metric nuts, which are rated by the numbers 4--8. A nut with a '6g' tolerance is the most common, with lower values indicating less tolerance, and high values indicating more tolerance for space between the nut and bolt threads.




The main variances in nuts are those with locking mechanisms and those without locking mechanisms. It would be impossible to create an unabridged listing of every type of nut available, but some of the most common are featured below.


Non-Locking Nuts


How to Select Acorn Nuts

Image credit: Fastenal

Acorn nuts have a smooth, capped recess that covers a threaded end. They provide safety and a finished appearance.                                 

How to Select Anchor Nuts

Image credit: Trade India

Anchor nuts expand so that a portion of the nut presses against a wall, securing hanging items with an anchor bolt.                                         

How to Select Barrel Nuts

Image credit: Win San Hardware

Barrel nuts have their threaded diameter perpendicular to its length. These are good for light loads and assembling sheet metal and furniture

Image credit: P-Wholesale

Cage nuts are square nuts inside a folded metal cage that can be compressed and released for incremental adjustment.

How to Select Coupling Nut

Image credit: Bangxin

Coupling nuts are long hex nuts used to join two threaded bolts or rods end-to-end. These are available without the hex profile.

Hot to Select Finger Nuts

Image credit: Finger Nut

Finger nuts (or thumb nuts) have a large inner to outer diameter ratio, enabling tightening by hand.


Image credit: etrailer

Handle nuts utilize a bendable handgrip so the nut can be positioned in hard-to-reach areas. The handle can then be removed. 

How to Select Hex Nuts

Image credit: Fastenal

Hex nuts have six-sided outer diameters, which is the optimal compromise between torque angle and footprint size.

How to Select Push Nuts

Image credit: Grainger

Push nuts are thin, non-threaded fasteners that are easy to install but difficult to remove. Flanges made of spring steel provide mechanical resistance.

How to Select Round Nuts

Image credit: Gasgoo

Round nuts are cylindrical in shape with slots on the outer diameter for tightening.

How to Select Square Nuts

Image credit: Allied Bolt Inc.

Square nuts have four-sided outer diameters for enhanced torque.

Image credit: Penn Engineering

Self-clinching nuts are held into sheet metal by a parallel squeezing force on the nut head. A serrated edge prevents nut rotation in the metal.

How to Select Washer Nuts

Image credit: Drillspot

Washer nuts have an attached washer. It can be free-spinning or stationary.

How to Select Weld Nuts

Image credit: U.S. Industrial Fasteners

Weld nuts incorporate a base so the nut can be welded to a substrate.

How to Select Wing Nuts

Image credit: U.S. Industrial Fasteners

Wing nuts are tightened by hand with two flanges extruding from the outer diameter. 

Image credit: Rick's Camaros

Lug nuts attach a tire rim to a vehicle axle. They have a tapered end.

How to Select Clip-on Nuts

Image credit: Aircraft Spruce and Specialty Co.

Clip-on nuts have a folded, metal plate base so it can be clipped to sheet metal.




Locking Nuts


How to Select Castle Nuts

Image credit: Fastenal

Castle nuts have slots parallel to the nut axis. Safety wire or a cotter pin threaded through the slots holds the nut in place.                                           

How to Select Flange Nuts

Image credit: U.S. Industrial Fasteners

Flange nuts have an enlarged circular base with a serrated face. This distributes load and prevents loosening.                           

How to Select Insert Nuts

Image credit: Home Depot

Insert nuts create a threaded socket in a wooden workpiece. Sharp flanges penetrate the substrate. They come in screw-in and hammer-in varieties. 

How to Select Jam Nuts

Image credit: Portland Bolt

Jam nuts are thin hex nuts that are run tight against a non-locking nut, preventing nut loosening.

How to Select Jet Nuts

Image credit: Zeckhausen Racing

Jet nuts are flanged hex nuts with an elliptical offset to lock the nut. The hex is thinner than a comparably-sized hex nut.

How to Select Kep Nuts

Image credit: Coburn Myers

Kep nuts have a free-spinning external tooth lock washer attached to one side of a hex nut.

How to Select Nylock Nuts

Image credit: FÖRCH

Nylon insert nuts utilize a bolt-tappable plastic thread insert that holds the nut tight.

How to Select Palnuts

Image credit: Aaron's Pushnuts

Palnuts are made of deformable spring steel that creates a resistant force. They function much like spring washers.

How to Select Speed Nuts

Image credit: Auto Body Toolmart

Speed nuts function as both a washer and lock nut. Two sheet metal prongs act as one female thread.

How to Select Split Beam Nuts

Image credit: Premier Screw

Split beam nuts have a split, tapered end that increases friction between the bolt and nut threads.

How to Select Tee Nuts

Image credit: Wikimedia

Tee nuts are embedded in a wood or composite material to provide a flush, threaded insert. Metal prongs penetrate the material. 



Locking Alternative


Two non-locking nuts, when torqued against each other, can provide a locking action. The inner nut is turned to half the approximate torque it can exert on the substrate. The inner nut is held in place while a second nut is added to the bolt, with full torque. This creates a firm, tensile stress on nut threads, locking them in place.




Fasteners sold in the North American marketplace that meet AMSE standards will be assigned an 18-digit PIN that will identify each unique piece of hardware. This is meant as a substitute for the traditional plain-text description of the hardware, which can be cumbersome.


Most metric fasteners conform to Deutsches Institut für Normung (DIN) standards. This is closely related to ISO production standards for metric nuts. Most hardware measured in imperial units is subject to Society of Automotive Engineers (SAE) edict. A manufacturer is not required to follow either guideline, but the hardware may be of less quality if they elect to dismiss these standards.


BS EN ISO 225 — Fasteners - Bolts, screws, studs and nuts - Symbls and descriptions of dimensions




U.S. Industrial Fasteners of Arizona Inc. - Nuts


Penn Engineering — Self-Slinching Nuts


Wikipedia — Nut (hardware); Unified Thread Standard; ISO metric screw thread


Engineer's Edge — Fastener and Screw/Bolt Design, Formula and Calculation


Bolt Science — Thread Tolerancing — Nuts



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