Lyman Pro Headspace Gauges have more features than any headspace gauge on the market! Inspired by the Lyman 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 Headspace gauges check maximum and minimum cartridge headspace as well as maximum case length. Headspace gauges are recommended when setting up sizing dies for any bottle neck cartridge.