Chicago Pneumatic P073942 Retainer Lock Spring, For Type/Brand/Model: CP 4181 Duler And CP 4181 Duser Rivet Buster, CP 4181 Puler And CP 4181 Puser Rivet Buster, CP 4608P And 4611P Handheld Pneumatic Rivet Buster, CP 4608D And 4611D Handheld Pneumatic Rivet Buster