The Wilson Case One piece gage will check overall length to indicate the need for trimming datum to head length to assure correct headspace and to prevent over sizing. Available for most popular rimless cases.MEASURES MIN/MAX CASE LENGTH AND MIN/MAX HEADSPACENote: Does not measure body diameters. This gage is intended to be used with fired cases to determine a basis for full length sizing and trimming.Made in the USA