This hub uses 608ZZ bearings to reduce friction. You need to make two of these to form a complete hub.The screw holes and the bearing socket may not come out the exact size you need because of differences in slicers and printers. I have made them a little oversize, so you should be able to assemble the system easily. The three screw holes near the center are for short #6 screws to be threaded in; their only function is to hold the bearing in place; use washers. The three screw holes near the perimeter are for long #6 screws, to pass through hub piece #1, the Taulman center web, and hub piece #2