1/4-20 Coin Door Whiz Flange Locknut
Ships from US and is sold by Pinball Life$0.19
This nut attaches the coin door frame to the cabinet. On Williams/Bally games (WPC/WPC era) it also attaches the hinge to the back box.
Used in conjunction with the 1/4-20 carriage bolt.
Williams/Bally reference #4420-01141-00.
Data East/Sega/Stern reference #240-5300-00.