Abstract: A tool for scribing a longitudinal groove on an elongate cylindrical rod suitable for implanting as a prosthetic in a living being supports the rod in a linear groove on a bed of a frame of the tool. A track is mounted on the frame and runs parallel to the groove. A carrier mounted on the track can slide on the track in constant spaced relation to and along the groove. A scribe mounted on the carrier extends toward the groove to contact a rod in the predetermined position. A preferred version of the tool has a clamp mounted on the bed for clamping the rod in the predetermined position. Additional features allow for precise angular positioning of the rod and for scribing a dashed line on the rod. In use, the tool operator places the rod in the predetermined position in the groove. The scribe is then pressed into contact with the rod. While the scribe is in pressed contact with the rod, the operator slides the carrier along the track.