Used Park Tool CRC-15 Crown Race Cutter Adapter bicycle technician tool.
From Park:
The CRC-15 is used in conjunction with the CRC-1 Crown Race Cutting Tool (not included) to machine 39.8mm crown race seats on forks with a 1 1/8" to 1.5" taper. Includes precision-machined adapter body and high-speed steel crown race cutter.
Tool is is very good condition, does not appear to have seen much use.