WWoooWW you lost me.. What do you have that uses a 6mm out put shat?? All motors that I’m aware of use 5mm / Mod one pinions gear.. We typical buy them from Mike (RCM)
http://www.rc-monster.com/gears.php
Regardless welcome to the forum.. You’ve tapped into the greatest group of gentlemen known to man kind..
Have a great one..