Screws keep loosening up.

[thompsoncustom]

Fill the hole with JB weld and then wipe the screw down lightly with grease making sure it's 100% covered but only vary thinly. Now put you screw in the hole and wipe off all the jb weld that squeezes out and let sit for 24hr. Screw might be a little tight the first time you break it loose but you will be good to go after that.

 

[mudrat2]

As I posted elsewhere:
Depending on type of plastic, one trick I use is put the screw in the hole and hold a hot soldering iron on the head until the plastic starts to melt. Carefully remove the iron without disturbing the screw. Let it cool then remove the screw. The melted plastic flows around the screw threads and hardens into good threads.

Sometimes I add slivers of similar plastic if the hole is really stripped out and the hole enlarged.

Works well on ABS and PVC, nylon may not flow depending on how old and moisture content.