Lex’s recent post on captive nuts reminded me of some other nuts I’ve been using a lot lately while doing some volunteer work on a search-and-rescue van: nylon-insert hex nuts. Depending on which big box you shop at, and whom you ask when there, they’re also called stop nuts, locknuts, or nyloks (although NYLOK® is a nylon material typically applied to bolts and screws), or nylocks. I like them because they resist vibration and loosening, they’re reusable, they don’t damage threads, and they’re readily available. McMaster-Carr has a large variety in their catalog, and many of the big boxes carry Hillman versions.
For higher vibration, temperature, or safety applications (like motorcycle and automobile racing or aviation), safety-wired nuts, or nuts with cotter pins are the preferred — if not required — choice. Other alternatives include two-piece thread-clamping locknuts and distorted-thread locknuts.
A 100-piece package of 1/4″-20 nylon-insert nuts will cost you around $5.