Abstract: A translating mechanism for accurately positioning and locking an object relative to a reference plane comprises a base plate which defines the reference plane and a platform supported parallel to the base plate for movement in a direction perpendicular to the plane of the base plate. A spring between the base plate and platform urges the latter away from the plate and an adjustment screw operably connected to the platform and to the plate permits changing of the spacing between the platform and plate against the bias of the spring. Nestable U-shaped arms pivotally connected to the plate and platform, respectively, and to each other directly slideably engage the plate and platform, and maintain parallelism therebetween during their relative movement. A flexible end wall adjacent to the platform releasably clamps the platform against the opposite end wall to lock same in any position within its range of movement. This also minimizes the load path length between platform and base.