SummarySteel balls are glued with epoxy to the part holes. Belts are fixed by placing a loop inside the slot and later inserting a piece of filament inside the belt in the loop to keep it from sliding out. Bill of materials Two 10mm steel balls. Four 15mm M3 bolts Four v-shaped bearings. Epoxy I got the extrusions from here: I Designed ThisI used Onshape to design these parts, you can find them as a public document there in case you want to edit them: