Re-use Of Fasteners
This is a terribly important topic, and you need to learn about it from someone who
knows a lot more about it than I do.
Here are some rules I live by, which are sure to enrage the AME's:
1) Flat washers can generally be re-used as long as they are not scarred or distorted.
Always use at least a flat washer with a nut.
For non-structural applications, I have had great success using those clear plastic
washers to stop screws vibrating loose.
2) Never re-use a flat star lock washer, either internal or external.
They are "use-once" like a condom. The same sort of guy that re-uses a star lock
washer would re-use a condom. Ugh.
Typically a lock washer will be used with a flat washer (eg on a magneto stud) to
reduce the probability of the nut backing off.
Always replace star lock washers with new and throw the old ones in the garbage.
Don't let the homebuilders get ahold of them.
3) Split ring lock washers can be re-used as long as they are not squished flat.
They must be perky, like a new pair of tits.
4) Fiber nuts and metal stop nuts can be re-used as long as they retain adequate
Any doubt in your mind, toss them in the garbage. Keep a good stock of the
common sizes of new ones on hand (#4, #6, #8, #10, ¼ inch).
Be aware that fiber nuts in high heat areas (eg forward of firewall, landing
gear) will have a shortened life and will probably need replacement each time.
Try not to use fiber nuts in high heat areas but depressingly, engine and airframe
manufacturers frequently do. Look at a new airplane sometime with the cowl off.
5) Bolts can generally be reused as long as they have not suffered plastic deformation.
If used with metal stop nuts, check for adequate meat left on the threads to help
retain the metal stop nut.
Again, any doubt in your mind, toss it in the garbage and use a new one. Again, the
key to success is to have a good stock of common AN hardware on hand.