How to Keep a Nut from Loosening
Vibration and thermal cycling loosen ordinary nuts over time. There are several ways to stop it, and they fall into two camps: friction (lock nuts, lock washers, thread locker) and positive mechanical locking (castle nut and cotter pin). This guide compares the methods so you can pick the right one for the joint.
The Methods, Compared
| Method | How it works | Best for |
|---|---|---|
| Nylon-insert lock nut | Nylon collar grips threads (friction) | General assembly, moderate vibration, under ~250°F |
| All-metal lock nut (Stover) | Distorted thread grips (friction) | Heat, heavy-duty, reuse |
| Serrated flange nut | Teeth bite the surface | Soft/thin material, built-in washer |
| Jam nut (double-nut) | Two nuts wedge on threads | Setting position, backing up a nut |
| Castle/slotted nut + cotter pin | Positive mechanical lock | Safety-critical, wheel bearings, aircraft |
| Lock washer (split / tooth) | Spring tension or bite | Light-duty supplement; least reliable alone |
| Thread locker (adhesive) | Chemical bond | When you can't change the nut; removable vs permanent grades |
Which Should You Use?
- Most jobs: a nylon-insert lock nut — simple, effective, one part.
- Heat or heavy-duty: all-metal (Stover) lock nut; nylon fails above ~250°F.
- Soft or thin material: serrated flange nut for built-in bearing and bite.
- Safety-critical or must stay serviceable: castle/slotted nut with a cotter pin — the only positive, non-friction lock.
- Can't change the nut: thread locker (blue = removable, red = permanent), or a jam nut.
For a deeper comparison of lock-nut styles, see our Lock Nut Comparison; for cotter-pinned nuts, see Castle vs Slotted vs Jam.
Frequently Asked Questions
What is the best way to keep a nut from coming loose?
For most assemblies, a nylon-insert or all-metal lock nut. For a positive lock that cannot back off — wheel bearings, aircraft, safety-critical joints — use a castle or slotted nut with a cotter pin. Match the method to the consequence of failure.
Do lock washers actually work?
Split and tooth lock washers add some resistance but are the least reliable method on their own, especially under heavy vibration. A dedicated lock nut or a cotter-pinned castle nut is more dependable. Use lock washers as a supplement, not the primary lock, on critical joints.
Is thread locker as good as a lock nut?
Thread locker works well when you can't change the nut, and it also seals threads. Use blue (removable) for serviceable joints and red (permanent) where you won't take it apart. For new designs a lock nut is usually simpler and cleaner; both can be combined for severe service.
Why do my nuts keep vibrating loose?
Either the joint isn't properly preloaded (under-torqued), or it's using a plain nut in a vibrating application. Torque to spec and switch to a lock nut, serrated flange nut, or a cotter-pinned castle nut depending on how critical the joint is.
Anti-Loosening Hardware in Stock
Lock nuts, flange nuts, castle/slotted nuts, cotter pins, and lock washers — from one source.