I bought a set of NEMA 17 motors off eBay assuming that they were 5 mm shafts. After i removed the pressed on pulleys I realized that they were 4 mm. So instead of redesigning and printing new pulleys for the Wade's extruder and Printrbot I am building, I came up with this idea.I printed this on a Makerbot Replicator 2 using the best setting. It took about 2 minutes to make 2 of them. I found that it was easier to slide the bushings on the motor shaft first (since it is designed to be very snug) then slide the 5mm pulley over it. You may use a drop of super glue to hold the plastic parts together, but I found that the fit is so snug that the grub screw was more than enough to keep it in place.