20 Common Nut Types: A Complete Identification Guide

Nuts are the unsung heroes of mechanical fastening. While bolts get the credit, it is the nut that provides the clamping force to hold assemblies together. With countless designs available, understanding the 20 most common types is essential for engineers, mechanics, and DIY enthusiasts. This guide breaks them down into three functional categories: general-purpose, locking, and specialty nuts.

The general-purpose family starts with the hex nut, the universal standard found everywhere. Its six-sided shape works perfectly with standard wrenches. For heavier loads, the heavy hex nut offers extra thickness and strength. The jam nut is half as thin and used as a backup to lock another nut in place. The flange nut features an integrated washer-like base that spreads pressure evenly, eliminating extra hardware. The cap nut, also called an acorn nut, covers the bolt end for a clean finish and safety. The coupling nut is a long barrel that joins two threaded rods, while the square nut, though older, still appears in track and machinery applications for its broad bearing surface.

Vibration loosens most nuts over time, which is why locking designs are critical. The nylon insert lock nut, commonly known as a nylock nut, uses a plastic ring to grip threads firmly and is both reliable and reusable. The all-metal lock nut achieves the same effect without plastic, making it suitable for high-temperature environments. The castle nut has slots for a cotter pin, offering absolute mechanical security in automotive and aviation hubs. The slotted hex nut works similarly with a split pin. The keps nut comes with a built-in spinning lock washer for quick assembly. The center lock nut has a nylon patch on its threads, while the two-way lock nut uses tapered threads to bite tighter under tension. Both are ideal for heavy machinery and high-vibration applications.

Specialty nuts solve unique problems that standard designs cannot address. The wing nut has large ears for hand-tightening, making it perfect for fixtures that need frequent adjustment. The thumb nut offers a knurled surface for finger-tightening in electronic enclosures. The tee nut sinks into wood with prongs that prevent spinning, commonly used in furniture assembly. The weld nut fuses to metal plates via spot welding, providing threads where backside access is impossible. Finally, the split nut comes in two interlocking halves for quick release without spinning, often used in lead screws and quick-change setups. From workshops to aircraft, these 20 nut types cover virtually every fastening need, ensuring safety, durability, and efficiency in any project.

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