Brown & Sharpe 599-792-9 4 Piece Edge Finder Set
Locate round or flat work easily within 0.0005". Fully hardened and precision ground. Rated up to 1,000 RPM. To use, just place in a standard 1/2" diameter collet or chuck. As the collet or chuck rotates and approaches the edge of the work, the head moves sideways about 1/32", and the center of the finder is exactly one-half of the head diameter away from the edge of the work.