3mm shaft diameter Brass and Hardened steel pinion gears now Available in Mod.3, Mod.4 and Mod.5 pitch These are sold 1 gear per purchase, Pictures for reference. 

These are press on gears, You must either use a pinion gear tool or know what you are doing to install these or you may ruin your motor. Use at your own risk and skill level.

These are for the largest motors such as the Mofo Rc SMP Pancake motor, Or the Furitek Komodo, And several other larger motors. The stock replacment gear for the pancake would be mod.3 18t or 20t, will fit up to 24t, or if mod.5 11t, 13t, or 15t, Or if mod.4 12T for use with the Redcat Ascent-18 or the Scx24 using a Mod.4 Steel Spur gear from mofo rc.