Types of Nuts: A Complete Guide
A nut is an internally-threaded fastener that mates with a bolt, screw, or threaded rod to clamp a joint. Beyond the standard hex nut there are dozens of types, each shaped for a job: resisting vibration, spreading load, joining rod, transmitting motion, or fitting where a wrench cannot. This guide walks through the main families and links to each one we stock so you can go straight to the right part.
General-Purpose & Structural
- Hex Nuts — the standard six-sided nut for general bolting, in Grade 2/5/8/9, metric, and many materials.
- Heavy Hex Nuts — larger, thicker pattern for higher loads and larger diameters.
- Structural Heavy Hex Nuts — A563 DH and A194 2H for A325/A490 structural bolting.
- Hex Jam Nuts — thin nuts that lock a primary nut or set position.
Locking & Vibration-Resistant
- Lock Nuts — nylon-insert (nylock), all-metal (Stover), serrated flange, and K-lock styles.
- Castle & Slotted Nuts — cotter-pinned positive locking for wheel bearings and aircraft.
- Flange Nuts — integrated washer face; serrated versions resist back-off.
- Speed Nuts — spring-steel push-on (Tinnerman-style) nuts.
Joining & Motion
- Coupling Nuts — long nuts that join two lengths of threaded rod.
- Acme Nuts — trapezoidal-thread nuts for lead screws and motion.
- Square Nuts — four-sided nuts for strut, masonry, and anti-rotation.
- Channel Nuts — spring nuts for strut channel.
Sheet-Metal, Finishing & Specialty
- Weld Nuts — welded to a panel for captive threads.
- Cap & Acorn Nuts — domed nuts for a finished, safe-edge look.
- Wing Nuts and Thumb Nuts — hand-tightened, tool-free.
- Tee Nuts — pronged inserts for wood and composites.
- Cage Nuts and Self-Clinching (PEM) Nuts — for racks, enclosures, and thin sheet.
How to Choose
Start with the function: general clamping (hex, heavy hex), vibration resistance (lock, flange, castle), joining rod (coupling), motion (acme), or sheet-metal attachment (weld, cage, PEM). Then match the thread and grade to your bolt — see our Nut Grade & Bolt-Matching Guide — and the material to the environment — see the Nut Material Guide.
Frequently Asked Questions
What are the most common types of nuts?
The hex nut is by far the most common, followed by lock nuts (nylon-insert and all-metal), jam nuts, flange nuts, and heavy hex nuts. Beyond those, coupling, acme, castle, weld, square, cap, and wing nuts each serve a specific purpose.
What type of nut keeps from coming loose?
Lock nuts (nylon-insert, all-metal/Stover, serrated flange, K-lock) resist loosening by friction or bite; castle and slotted nuts with a cotter pin give a positive mechanical lock. See our guide on keeping a nut from loosening.
What nut is used to join two threaded rods?
A coupling nut — a long hex nut that each rod threads into for full engagement. Reducing coupling nuts join two different thread sizes.
What is the difference between a finished hex nut and a heavy hex nut?
A heavy hex nut is wider across the flats and taller than a finished hex nut of the same thread, giving more bearing area and strength for larger and higher-load joints.
One of the Deepest Nut Selections in the Northwest
Every type above, in steel, stainless, brass, bronze, and more. By the piece or in bulk.