Moore & Wright - Ext Micrometer 0-25mm Carbide (MB-200-01) Small Base The sliding Die Chamber has

The sliding Die Chamber has a concentric bullet channel just slightly larger than the bullet diameter

A special fine thread is used to attach them to the gauges

Add the interchangeable heads HERE

The calibrated flange acts as an overlay that clearly shows if the edge of the bullet hole touches the higher scoring ring

Moore & Wright - Ext Micrometer 0-25mm Carbide (MB-200-01) Small Base The sliding Die Chamber hasOutside Micrometer 0 25mm Range 0 25mm Resolution 0. 01mm Hammertone finished frame with insulated grip Satin chrome scale Tapered for easier access to difficult areas Packed in plastic box with standard and adjusting key