The http://mendel-parts.com V9 1,75mm Hotend/Extruder works reliable as it is, but it has some downsides.It uses a brass drive gear which is not very reliable. If the filaments runs out or snaps the teeth of the brass drive gear touch the hardened steel surface of the bearing and become dull.Also filament change is complicated and time consuming. It is often necessary to disassemble the screws that hold the springs if you don't have 3 hands. ;-)The MK7 Drive Gear is a useful upgrade. It has a better grip on the filament, is made from stainless steel and makes filament change easy.The enhanced driveholder guides the filament more reliable and can be fixed down to the lower aluminum plate to increase stability.To fit the MK7 Drive Gear on an V9 Extruder some modifications are necessary:Optional:See http://www.thingiverse.com/thing:16319 for the optional filament guide which is useful for printing with 1.75mm ABS.You can now insert the filament by slightly pushing it in and turning the wheel. It isn't necessary to press against the springs anymore.Comments/suggestions are appreciated.