I'm having trouble finding a 5mm 24t pinion that will mesh with a 54t jato spur for my e revo. I've heard that Robinson Racing has pinions that work, but I'm not sure which of there pinions are 5mm?
The ones which say '5m/m bore' funnily enough- you want the mod 0.8 ( module 0.8 ) pinions; click products, then the 'brushless motor pinions' at bottom-right are what you want. Rc-monster.com also sell suitable pinions, best available I would argue.
Keeping the Mods busy is my specialty...