BTW if you guys are looking for good sources for gears, I use MOD1 for all the heli engineering I do and sdp-si.com has a great source and catalog of all metric stock drive gears and pulleys etc. THey have tons of 5mm bore mod 1 gears that could replace the stock spur and bolt directly onto the input shaft of the stock revo gearbox (which is 5mm incidentally).

Mod 1 refers to the standard spacing between teeth which is largely greater than 1mm, if you look at the PDF drawings of some of the gears on sdp-si.com you can see the measurements for your self.

Hope that helps...