Hornady Lock-N-Load Headspace Gauge 5 Bushing Set with ComparatorThe Hornady Lock N Load Headspace Gage is a great tool for increasing the accuracy of your loaded ammunition. The Headspace gage measures from the case head to the datum line on the case shoulder to allow proper brass resizing for a precise fit with the rifle chamber. Bushings fit the comparator body and attach to calipers with a thumb screw. Can be used with bottleneck cases from 17 caliber through large belted magnums. Function: To measure from the