Abstract: A drill guide apparatus for use in drilling a central bore in a portion of a broken-off bolt remaining in a threaded bore. A clamp tube carries inwardly-directed setscrews for attaching the clamp tube to a stud or bolt located near the broken bolt. An arm extends adjustably through the clamp tube, and setscrews in the clamp tube hold the arm in a desired position relative to the clamp tube. A drill guide holder mountedon the arm includes setscrews which hold an appropriate drill guide tube in position to receive and guide a drill to bore the required hole in the remaining portion of the broken bolt.