i built the first one and used a mk8 gear . It worked great but needed a torquey nema17 to make it work.. recently i needed a extruder and got hands on a bic lighter.. i made the extruder using a small 34mm nema17 ... this thing has got loads of torque and no stripping of the filament.. i think this is one of the most brilliant extruders i have used. Only thing is loaded filament is a PITA. great work! .. thanks.