Manufacturer: Tedd Cash Manufacturing Co.
Part Number: TDC-BG-3
Description: Copied from an original. Easy-to-read numbering. One side measures caliber from 15 cal up to 80 cal. The other side measures shotgun bore sizes from .410 to 10 gauge along one edge, the other edge is calibrated in metric bore sizes, from 5.5 mm to 11 mm. You'll be surprised how handy it is, and how often bore size is in doubt.