Link 1, which is the ball-bearing nut, has recirculating channel 2 filled with balls. As ball-bearing screw, link 3, is screwed into link 1, the balls roll along the thread which is in the form of semi-circular grooves in both the nut and screw. At the end of the nut the balls run back into recirculating channel 2 and through it to the beginning of the nut again. Thus sliding friction is replaced by rolling friction, thereby substantially raising the efficiency of the screw. With respect to each other, links 1 and 3 accomplish a helical motion about and along common axis y-y.
$54$EM,KP$