Nylon Screws

In the game manual, it states:
<R7> Robots are allowed the following additional “non-VEX” components:
c. Any commercially available #4, #6, #8, M2, M2.5, M3 or M4 screw up to 2" long, and any
commercially available nut and/or washer to fit these screws.

Does that mean it is legal to use nylon screws as they are commercially available?

Yes, this is legal, provided they fit within the restrictions listed in the above quoted rule.