New sheridan 12 gram seal, one included.
These work in standard classic Sheridan 12 gram valves or newer Sheridan Cartridge valves.
They work in the follow Sheridan paintguns including the PGP, PMI 1, P-68sc, PMI df, KP-2, K2, K1, KP3s, Annihilators, some vipers, pursuit pistols, P-12, palmers 12 gram paintguns and others I am probably forgetting about.