The TSS Hexagonal Headspace Datum Shoulder Bump Comparator Tool represents a premium all in one tool, ready for a lifetime of use. This tool functions like the other headspace-shoulder bump comparator measuring tools on the market, but this one combine everything into a rigid one-piece tool made from stainless steel. There are no bushings to swap or lose, and the design protects all critical surfaces from abuse! How to Use: 1. Determine the shoulder datum diameter you want to use 2. Orientate the comparator so that the desired shoulder diameter size is at 6 O'clock, and facing the bottom moveable jaw of the caliper 3. Move the brass thumb screws to the opposite side of the intended diameter size of the hexagon to engage the fixed top jaw 4. Snug down brass thumb screws to the fixed top jaw of the caliper 5. Close the caliper jaws and zero the caliper 6. Ready for use!