This spring fits around the pop bumper plunger and pushes the ring & rod assembly up.
Also used on some Williams flipper mechs & slingshot assemblies, 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 #13-7005-00 & 13-007005-00.
American Pinball reference #SPR0005-00.