After a case has been loaded a few times, it will stretch beyond maximum length and must be trimmed. The Case Length Gauge (Pilot) and Shell Holder are Specific to each Cartridge. Trimming cases eliminates the danger of excessive case length. Trimming squares the mouth of the cartridge for a more accurate bullet seating. The Case Gauge requires a Lee Cutter and Lock Stud LEE 90110 to function correctly.