Duane is right about the rubber like stuff you can paint on the threads. That was a treatment we used to use in the machine shop......Has any one thought about precision cross threading, metric bolt with SAE thread, beating the threads on the bolt with a hammer, etc ?....Just kidding !....Precision sheet metal shops have locking blind nuts of various styles that press in. Some have very precision, GH1 to GH5 fit, hardened or soft threads etc. Some feature all metal locking threads that are a little distorted to make them lock, and some simply have nylon locks with metal threads just like the nylon lock nuts. Years ago I tried aluminum 1/4 20 bolts for wing bolts, but soon found they vibrated loose too easily, and were unsafe for high vibration applications. I would not consider using a metal bolt without some sort of vibration protected locking system, but there are many ways to do it.....
