The present invention is a self-locking internal adapter for D-shaped orthopedic tools. A locking ball mechanism prevents movement of the adapter components relative to each other, while a plurality of securing ball mechanisms releasably secure a D-shaped orthopedic tool in the adapter. A chamfered surface of the adapter engages a chamfer of the tool to centrally stabilize the tool in the adapter. The internal adapter may be used with driver handles, ratcheting handles and torque-limiting handles.