A z-coupling that eliminates slipping.Has a set screw for the motor shaft and captive nut for the 5/16 threaded rod.1) Thread a 5/16 nut about 1 inch down the Z threaded rod. 2) Insert another 5/16 nut into the coupling nut retainer. 3) Thread the rod into the coupling, all the way in until it stops. THis threads the shaft into the plastic past the captive nut. 4) Optional - Apply low strength thread locker on the shaft below the captive nut. 5) Tighten the locking nut onto the captive nut. 6) Install a 6-32 nut into the retainer at the 5mm end of the coupling. 7) Screw in a 6-32 bolt or grub screw. 8) Install assembled rod into X-end. 9) Slip the 5mm end onto the motor shaft and tighten set screw. *If your motor shaft does not have a flat surface, make one with a dremel w/ cutting wheel.