The idea is get the leadscrew into the coupler when installing about 1/2 into the coupler, tighten the setscrews to it. Now slide the coupler over the motor shaft until the 2 shafts mate inside the coupler. Now using your hand or just the hex key in the setscrew of the motor half side of the coupler, slightly stretch it down and tighten in the slightly stretched position. This pretensions it so that the 2 shafts are pulled together with force.