I noticed the original pulley on my printer wasn't drilled in the center -- creating a wobble and therefore printing problems. I printed the pulley and when installed the wobble was less pronounced. After the 3rd iteration it was running completely true. Note the 4mm setscrews have nuts that are inserted into the slots at the end of the pulley and they are opposing one another which mitigates distortion when they are tightened. Number of Teeth: 10 Shaft Diameter: 5mm Outside Diameter: 15 mm