The Lee Precision kit combines a Case Length Gauge and a Universal Shell Holder for reloaders of the 9mm Luger cartridge. The hardened steel gauge serves two purposes: by itself, it can be used to quickly check if a case has stretched beyond its maximum safe length. When combined with a Lee Cutter and Lock Stud (sold separately), it also acts as a pilot to trim cases to a uniform length without needing to take any measurements. Including the correct shell holder makes this a great value. Trimming 9mm cases to a consistent length is key for applying a uniform taper crimp on every round, which leads to more reliable feeding and better accuracy in semi-automatic pistols.