These Ammo Checkers are gauges that allow a reloader to quickly confirm that their ammunition will fit in their chamber. Machined from solid blocks of 6061 T6 aircraft grade aluminum and cut with custom tooling to SAAMI minimum chamber dimensions. One gauge will work with a variety of calibers. Just drop your loaded rounds into the ammo checker, and if the round fits into the gauge, it will fit in the gun's chamber. Each caliber is clearly engraved on the gauge. Bright orange anodizing makes them easy to find on your reloading bench.