Allows the user to trim cases by hand or with a power attachment (included) to precise pre-set length. No adjustment of measuring needed. Trimmer comes with a case locking device cutter trim-to-length pilot cutter head and both hand and power trimming adapters. Trimmer works with any standard shellholder including Lyman Redding RCBS Hornady and Lee Precision. Assembles in seconds and you are ready to trim cases.