Replicator MK8 spring loaded filament drive. imported originals into sketchup so I could edit sizes a bit to fit 5x10x4 bearing I had. tidied up model after import and got all holes bang on size. Already printing Right drive with constructed left.Adjusted printed parts for standard socket allen bolts. I got some 4mm x 0.5mm brass tube to make a shoulder allen bolt, seems to work fine. I had some 40mm x 9mm springs that I cut in half to use. guessing the force is ok as it seems to be printing fine.