Quite often, generic screws have a smaller thread. That way they fit most nuts and tapped holes, even ones that have threads that are damaged or dirty. The amount of play is especially noticed when screwed into a generic loose threaded hole.
The fit of the threads determine whether the screw will back out. If the nylon threads are just as loose as the metal threads, then they will back out too. The secret is to find screw threads that are oversized for the hole threads. That way, the nylon ones can be squeezed into the tight threads and still be adjusted easily. Metal screws cannot be forced into threads that are too small, but the proper fit can be very tight.
Except for the Automag in front, its usually the man behind the equipment that counts.