This spacer by Aimpoint fits AimPoint CompM4 and Aimpoint CompM2/M3. Mount raises height of optical axis from 30 to 39 mm. This Aimpoint Accessory works n conjunction with Aimpoint 30mm SightTop Ring for QRP2. This red dot sight accessory boasts the same Aimpoint quality as we have come to expect from Aimpoint Red Dot Sights. This Aimpoint Red Dot Sight Accessory is made to work with the Aimpoint Red Dot Scopes.