Stock and Aftermarket Sheridan back tube plugs and RVAs (Rear Velocity Adjusters). The stock Sheridan part number for a back plug is: HB17-037 retaining cap These rear caps will work on most Sheridan 12 gram based pump paintball markers and air guns such as the PGP, PMI 1, P68-sc, Pursuit Pistol, Mac 1 Annihilator and EB pistols.