An adjustable depth drill bushing assembly in which the concentricity of the drill bushing and the mounting bushing is maintained by providing flat cylindrical mating surfaces between the drill bushing and mounting bushing, even when threads are present in the mating area. Cooperating structure is provided between the two bushings which permits both precise axial adjustment and rigid interengagement. The drill bushing is adapted to move axially of the mounting bushing in the released configuration, and is rigidly locked in place in the engaged configuration.
