A locking instrument assembly for use in conjunction with an intramedullary device is disclosed. The locking instrument assembly includes an inner collet, an outer body, and a knob. The inner collet has a collar and a fastener member. The knob engages the fastener member to press the outer body against the collar. As the knob mates with the fastener member, the collar applies a clamping force to the intramedullary device.