Abstract: Apparatus for assembling different size parts in a vertical assembly is provided which includes a pair of fingers attached to and extending from the gripper of a manipulator in parallel relationship and moveable toward and away from one another under control of the gripper. Different diameter curved outer sections extend around the periphery of and are stepped along the length of the fingers. The smallest diameter curved section is located at the outer end of the fingers and successively wider diameter sections are located along the fingers as the inner end is approached. One of the predetermined diameter sections has a predetermined slope, each part to be assembled has an opening therein of a diameter slightly larger than a diameter of a section of the fingers along the length thereof.