Delta model 17-935 Mortising attachment, New never out of case.1/4”, 5/16”, 3/8”, 1/2” mortising chisel/bit set. Fits Quill diameter 1 1/2”, 1 7/8”, 2”, 2.6”/ Delta and Sears drill presses. Cut perfect square holes for precise mortise and tenon joints easily and quickly.