The Accu-Ring is a sizing/seater die lock-ring which provides reference marks in increments of thousandths of an inch (0.001"). Sizing die (primary use) - Designed mainly for sizing dies, the Accu-Ring helps you zero in on what you want the headspace length of your cases to be. Seater die (secondary use) - The Accu-Ring also allows you to make fine adjustments to bullet seating depths. Notice: The distance of 0.001" is the distance between a long and short reference mark as shown in Figure 1. This distance indicates the up or down adjustment of the die in the Co-AxA(R) Reloading Press. Actual up or down movement of the die is 0.000998" per refere Mfg: Forster Products, Inc.