mamba motor shaft pinion size?

hi. new to this forum, but gotta say it is an awesome one. My situation is that i'm getting a crt .5 with an electric conversion kit and will be running my 5700 mamba max. My question is what size mod1 pinion would i need to run with it? I don't really have anything to measure the shaft. i did a search but didnt see the answer so was just wondering if i would need to use the 1/8" bore mod1 pinion or a 5mm mod1 pinion. I'm sure its a stupid question but i have no clue how to figure it out. Thanks for any help.