For a tight fit that won't come free when vibrated, form threads into these nuts. Because they are only partially threaded, the tightening motion will cut the remaining threads when you secure them to metal screws. Although nuts can be reused a few times, their holding power diminishes with each usage.
Nylon 6/6— These nuts thread on smoothly, withstand normal wear and tear, and are abrasion-resistant and slippery. Nylon works best in dry conditions because it will bloat and weaken in wet conditions.