You can get MK8 Drive Gear (from any seller) or if you are in US get the hobbed pulley from trinity labs.
If you can select prefere pulleys which can be mounted on M8 screw since most geared extruders use M8 screw.
But there are also some which use Φ5mm shaft or M5 screw (but I had a problem to buy M5 screw localy which would really have 5 mm diameter).
You will need to adjust OpenScad file of some extruder to set gear ratio you want.
You must pair extruder you like with the driving gear.
Some extruders do not need drive gear, they use M8 hobbed bolt. You can do your own hobbing with a dremler tool. The hobbing can be on the bolt body or on its head (M8 bolt with head for hex key). The second one is probably better because it has bigger diameter.
If you have some uncommon spare ball bearings (compared to the common 608 or 629) or driving gear and want to use them (instead of buying/making the right ones for the extruder of your selection), then I have a parametric geared extruder where about 40 parameters can be set. If you want it let me know and I'll post it.
If you can select prefere pulleys which can be mounted on M8 screw since most geared extruders use M8 screw.
But there are also some which use Φ5mm shaft or M5 screw (but I had a problem to buy M5 screw localy which would really have 5 mm diameter).
You will need to adjust OpenScad file of some extruder to set gear ratio you want.
You must pair extruder you like with the driving gear.
Some extruders do not need drive gear, they use M8 hobbed bolt. You can do your own hobbing with a dremler tool. The hobbing can be on the bolt body or on its head (M8 bolt with head for hex key). The second one is probably better because it has bigger diameter.
If you have some uncommon spare ball bearings (compared to the common 608 or 629) or driving gear and want to use them (instead of buying/making the right ones for the extruder of your selection), then I have a parametric geared extruder where about 40 parameters can be set. If you want it let me know and I'll post it.