Abstract: A pin for insertion in the intramedullary passage of a broken bone has two generally tubular outer parts for insertion into the respective parts of a broken bone from an incision at the break, each having tapping threads along the distal end thereof and following threads along the proximal end thereof. The outer parts each have a reduced central axial hole which is square along a portion of both the distal and proximal ends thereof. The third central major part is a rod substantially equal in length to the combined lengths of the outer parts and having a cross-sectional configuration substantially conforming to the square portion of the axial hole of the tubular parts for a slide fit therethrough. One end of the central part has a recess in one end containing a spring pressed locking ball projecting outwardly from one side thereof and one or both tubular parts have a recess therein adapted for locking engagement with the spring-pressed ball when in register therewith.