This spring is used in a number of positions. It fits around the pop bumper plunger and pushes the ring and rod assembly up.
Also used on some Williams flipper mechs as well as other various assemblies.
Williams reference #10-135.
Bally reference #SP-200-180.
Stern/Sega/Data East reference #266-5047-00, 266-5020-00.
Jersey Jack Pinball reference #13-007002-00.
American Pinball reference #SPR0005-00.