"Lloyd E. Sponenburgh" lloydspinsidemindspring.com prodded the
keyboard

John G fired this volley in
:

So what the locking eqivelant in nylon nuts or isn't there one,
just do them up tight?

A hot implement poked just a shallow bit into the outboard junction
between nut and screw, so that both are melted and deformed at the
spot.
Depending upon the size, maybe three such spots. Don't go too
deeply into the nut, as the number of threads in engagement is
pretty important with plastic screws.

The tip of a very small soldering iron works, but it smutches up the
tip. I keep one with a 1/16" screwdriver tip around just for tacking
and piercing plastics. (have another for soldering, and it never,
ever touches thermoplastics)

Lloyd

I agree ! I've used the hot wire technique many times,
though "Loctite" make a thread locker for plastics.

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Best Regards:
Baron.