Williams/Bally #2-56 x 7/16" Microswitch screw and Locking Washer
Ships from US and is sold by Pinball Life$0.15
This small mounting screw is used to mount many different microswitches to various mechanical devises and brackets both above and below the playfield.
Comes with locking washer.
Williams/Bally reference #4002-01105-10.