Minimalist one piece extruder drive, using elastic bands for tensionPrinted at 100 % infill, 3 walls 0.5 mm tip. I think if I re-print version 2, I would only use 2 walls, because the way SLIC3R does fills etc. I designed it for Bearing, Dimensions: 8mm x 22mm x 7mm/Metric ID (inner diameter)/Bore: 8mm OD (outer diameter): 22mm Width/Height/thickness: 7mm Also known as 608-2Z ball bearing. And a serrated shaft adaptor i found in Technobots http://www.technobotsonline.com/universal-coupling-insert-5mm.html On version two, there is a second pair of 'lugs', to alow 3 different pull force, Note on version one, the elasiic band can slip off, so I shamfered out a small weadge,to help keep it in place. I hopefully have left enugh space (on v2) for a 4mm phenumatic fitting. Note, possably not so obvious from photos, The flat (printbed) side is uppermost, pictures are for illistration - only. Enjoy Ceri