Abstract: A locking hydraulic actuator has a cylinder and a main piston that is movable from an extend position to a retract position by a hydraulic circuit. The actuator has a locking mechanism that includes a lock piston that slides within a lock piston bore of the main piston. One or more lock segments are held by slots within the main piston and may be radially constrained within a tailstock housing and cylinder. The lock segments maintain the main piston in a locked position. The lock segments have two straight tapers, one on a proximal face and the other on a distal face, which transmit axial loading forces to and from the cylinder and main piston by distributed loading, thereby avoiding point-contact loading and material deformation. The lock piston, lock segments, piston, and cylinder may have different hardnesses.