10 count bag of Hard Polyurethane Tank O-rings will work on any standard paintball marker's Co2 tanks, HPA tanks, ASA, and on various marker parts that are the same size. Keep well lubricated for best performance. The hard o-rings are much more durable than rubber polyurethane o-rings. It does not stretch, expand or swell up like rubber polyurethane o-rings. Made for hundreds of uses before needing replacement.