The Hornady Rim Thickness Gauge is perfect for rim fire enthusiasts who demand nothing but the utmost consistency. The gauge allows the shooter to sort ammo by the rim thickness to find all ammunition that has similar ignition qualities to improve accuracy. This gauge attaches to a set of calipers and will measure the rim thickness on 17 and 22 caliber ammunition. Fits: Any 6" dial caliper Notes: Includes bushings for use with all 17 and 22 caliber ammo