Hex Nut vs Nyloc Nut — Which One Should You Use?

Hex nuts are the standard six-sided threaded fastener used across virtually every industry. They rely on friction between the mating threads and a clamping force generated during tightening to stay in place. A plain hex nut does not have any built-in locking mechanism — it relies entirely on correct torque and, where needed, a separate locking device like a spring washer or thread-locking compound. Hex nuts are available in mild steel zinc-plated, stainless steel SS304, brass, and nylon at ScrewBazar in all standard metric sizes.

Nyloc nuts (also called nylon insert lock nuts) have a standard hex body with a nylon collar embedded in the top. When the bolt is driven through the nylon collar, the nylon deforms around the thread and creates a prevailing torque that resists loosening. This locking action works independently of bolt tension — the nyloc nut resists vibration even if the joint loses some clamp load. Nyloc nuts are one-use fasteners by design; the nylon insert loses its locking effectiveness after a few removal and refit cycles.

This is where hex nut vs nyloc nut performance diverges most clearly. A plain hex nut under vibration will gradually lose the friction that holds it in place. Without a spring washer or thread-lock applied, it can work loose. A nyloc nut maintains its prevailing torque regardless of the bolt tension state — the nylon insert keeps the nut from spinning back even as vibration tries to unwind it. For any assembly subject to regular vibration — machinery, automotive suspensions, pumps, compressors — a nyloc nut is the safer choice.

The nylon insert in a nyloc nut has a temperature limit. Standard nyloc nuts should not be used above 120°C — the nylon softens and loses its locking function. For high-temperature applications (exhaust systems, engine bays, industrial ovens), a metal lock nut (all-metal prevailing torque nut) or a plain hex nut with a thread-locking compound rated for high temperature is required. Hex nuts have no such temperature limitation in themselves — their material grade determines the temperature limit, and stainless steel hex nuts are suitable for several hundred degrees Celsius.

Plain hex nuts can be removed and reused many times — they're the standard choice wherever joints need to be disassembled regularly (maintenance panels, service access covers, adjustable assemblies). Nyloc nuts should be replaced every time they're removed; reusing a nyloc nut risks relying on a compromised locking insert. In high-volume assemblies this reusability difference can affect lifecycle cost. For permanent or semi-permanent connections where vibration is a concern, the nyloc nut's slightly higher unit cost and single-use nature is easily justified by the reliability it provides.

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Use a hex nut when: the joint is non-vibrating, joints are regularly disassembled, a separate locking device (spring washer, thread-lock) will be used, or operating temperature exceeds 120°C. Use a nyloc nut when: the assembly is subject to vibration, the joint is semi-permanent (infrequent disassembly), operating temperature stays below 120°C, and you want self-locking without separate accessories. ScrewBazar stocks both hex nuts and nyloc nuts in stainless steel SS304, zinc-plated mild steel, and brass.

Both nut types have flange variants worth considering. Flange hex nuts include an integrated washer surface that distributes load and reduces surface damage — useful when tightening into softer substrates. Flange nyloc nuts combine the load distribution of a flange with the vibration resistance of the nyloc insert, making them popular in automotive and machinery applications. Ask ScrewBazar about availability when placing your order.