The Hornady Lock-N-Load Concentricity Gauge identifies and eliminates bullet runout, otherwise known as, "wobble". With your ammunition placed in the tool, simply roll the cartridge to identify the amount of runout. Dial thumbscrew is used for adjustments. It has a sturdy frame and is easily mounted to your workspace. Specifications: Provides improved accuracy for handloaders Can be used to true up factory ammo Easy-to-use precision adjustment knobs allow you to true up the runout on any cartridge