Abstract: A mechanical clearance control apparatus operable for controlling the clearance between the rotor blade tips and the casing shroud of a gas turbine engine employs a radial adjustment mechanism. The adjustment mechanism includes an externally threaded hollow adjustment bushing disposed over a screw and rotatably and threadably coupled to an internally threaded bore of a stationary casing-shroud mounting section. Rotation of the bushing relative to the mounting section bore produces axial movement of the bushing relative thereto. An annular shoulder and a snap ring on a screw permit the bushing to rotate relative to the screw and carries the screw along with the axial movement of the bushing. One of several holes in the bushing rim can be aligned with a selected one of a pair of holes in the mounting section and a locking pin inserted in the aligned pair of holes to lock the sleeve to the stationary mounting section.