Leupold's Quick Release Mounting System allows the shooter to remove the scope with just a twist of the levers and reinstall it in only seconds with no loss of zero. Rings are made of Steel and sold in pairs. Extension Rings include one standard ring and one that is extended 5/8" to allow mounting of a wide variety of scopes. Mfg: Leupold Ring heights measured from top of base to center of ring. Super Low; .550" (14mm). Low; .650" (16.5mm). Medium; .770" (19.5mm). High .900" (22.8mm), Super High; 1.0" (2.5cm)