Grab the pulley assembly and begin to work the rope over the wheel bearing. Pinch the rope with a finger nail into the gap between the wheel and idler. Start to rotate the wheel so the rope is guided onto the groove. Fit the rope onto the wheel and place the idler assembly over the aluminum extrusion. The idler cap is designed to fit into the profile of the extrusion. Make sure the orientation idler matches with the rope and drive hub.
Press the idler onto the tip of the extrusion so it caps it off. If the idler doesn't freely slide in, the oval t-nuts might be to be adjusted so they can fit through the t-slots on the extrusion.
Adjust the screw and unfasten to loosen the t-nut if needed. The t-nut is not 100% required - The pulley can function without it, just won't be as secure with it installed. Once it's properly installed, the screw and t-nut can be tightened to secure the idler to the extrusion.