This is the Coats Jewel and Pivot Gauge. This tool was patented April 28, 1908. This tool can be used to measure both jewel openings as well as pivot sizes. There are 14 pivot sizes as well as 14 matching jewel sizes. Sizes range from 8 to 21. These are in hundredths of a millimeter. This is a very useful tool when working on pocket watches and it makes proper selection of jewels and staffs very simple.
