Abstract: A structure providing minimum fit mounting and rigid locking of a worm and gear drive includes a gear rotatably supported to a base, a worm drivably engaging the gear and bearings supporting the worm for rotation about its axis. A housing supports the worm bearings and is itself rotatably supported to the base for rotation about a second axis, which axis is parallel to but eccentric from the worm axis. Means are provided for pivoting the bearing housing such that the eccentricity of the pivot axes causes the worm to move toward the gear for close mounting and/or rigid locking therebetween.