This piece allows you to use a 20 tooth gt2 drive gear for the OB1.4. I have also used this for the rear idler by breaking off the support at the back of the idler to allow the belt to wrap directly around. This clips in so no need to disassemble the printer to use this.BOM: 20mm (I think) m3 screw 4 - 623 flanged Bearings 4 - m3 washers 2 - m3 Nut ( I used nylock ones because I just had them lying around)