the Lee 6mm PRC Case Length Gauge is a precise easy way to trim to length and square the case mouth. Use with the Case Conditioning Kit Cutter and Lock Stud or 3 Jaw Trimming Kit.The Lee Case Length Gauge and Shell Holder comes in a wide variety of sizes to accommodate all of the most popular cartridge calibers. This set of tools is made from hardened steel to ensure a lifetime of durable performance and is precision-crafted to tight SAAMI specifications.The shell holder is used to hold the case firmly in place during this operation and while using your Lee Case Trimmer Cutter. These tools help to ensure the maximum level of accuracy in trimming and squaring your brass cases.