This RCBS 45-100 2.6" caliber Trim Die doulbes as a visual case length gauge. Run a case into the Trim Die and if the case sticks out above the die's top then it is too long. File the case down until it is flush with the top of the die, then deburr the case mouth with a deburring tool. RCBS Trim Dies are precision machined, case hardened, hand polished and heat treated to withstand a file bearing against the toop surface without damage to the die. Standard 7/8"-14 threads. These dies are quite useful when a considerable amount of material needs to be trimmed off in your reforming operations, and should be used after you use any forming dies.