This RCBS Trim Die for cases 40-70 2.5" doubles as a visual case length gauge. Run a case into the Trim Die and if it sticks out the die's top then the case 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 top surface without damage to the die. Standard 7/8"-14 thread. 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.