This set of inserts was designed to be used with the EGW HD Tactical Rings, and will also work in EGW Practical Rings. The inserts are double rimmed to ensure that no slip takes place. EGW has done testing in their facility and have never had any movement of a 26mm scope when used with EGW rings and these specially designed inserts. Made from Delrin. Black in color. 2 per package (4 pieces total). Mfg: Egw