Recirculating ball screws have significantly less friction than leadscrews because they replace sliding friction with considerably lower rolling friction. A recirculating ball screw drive consists of a motor-driven screw with a nut coupled to the sled of the stage. Balls in a closed circuit are located between nut (ball case) and drive screw. Backlash can be minimized by selecting the proper ball-to-thread-diameter ratio. Recirculating ball screws are not self-locking but very efficient and offer high velocities and long service life in continuous operation. PI uses pitches of 0.5, 1 or 2 mm/revolution.