I dropped the damn thing into my engine bay and i cant find it. I know I was using a 12mm socket to remove it-- can anyone tell me what the inner diameter is? Nothing in my garage is metric and will fit the bolt on the terminal.

Also, is there any harm in loosing this nut in my bay? I know people were saying loosing the gaskets on the air intake could mess with the belts.. But i imagine a nut is much heavier than a gasket and will fall out eventually.

 

Personally, I would remove the nut on the positive side and take it to Home Depot. They have that display for screws and nuts so that you can reference (by installing your nut on the screws) to determine the correct size and thread pitch. It has saved my life quite a few time (I really need to buy a thread gauge).