3/8" 375-2M NATIONAL 3 SPLINE BACK SPOT FACER PILOT MT2
REVERSE SPOT FACER HOLDER. For use holding inverted spot facers or countersinks with #312 (5/16") National 3-spline drive. Arbor is #2 Morse taper shank. Made by National, patent 2120623. Marked "C", "X" and "1685C".