A substrate transport apparatus including, a torsional motion driver member having an exterior perimeter circumscribing an axis of rotation of the torsional motion driver member, and a torsional motion follower member including a body portion and a bearing collar rotatably coupled to the body portion, the torsional motion follower member being coupled to the torsional motion driver member with a dimensionally substantially invariant interface, wherein the bearing collar is decoupled from the exterior perimeter of the torsional motion driver member so that the exterior perimeter, as a whole, is free of the bearing collar.