Lyman Pro Maximum Cartridge Gauges have more features than any cartridge gauge on the market! Inspired by Lyman's Pro Die Sets, the gauges are precision machined from corrosion resistant stainless steel for a long rust-free life. The outside flats prevent rolling, and the o-rings provide a non-slip grip. Pro Maximum Cartridge Gauges check pistol ammunition for case length, diameter, and overall cartridge length. This inspection is considered mandatory by top competitive shooters who demand 100% reliability for their competition ammo.