Can someone tell me the size of the bolt that is used with the battery hold down bracket.
I have an M8 1.25 coarse thread and a M8 1.00 fine thread. Neither one seems to turn in. Maybe the threads in the nut are filled with paint or crud? Thanks for your help.

The ONLY place on your car that uses an 8x1 thread is the valve adjusters, if you have 8mm adjusters. All other 8mm hardware on the car is 8x1.25. Might want to run a tap through the hole before trying again. BTW, you should always give us the year and equipment of any car about which you're seeking information. Makes it easier to give you the right answers! The Cap'n

Yup, M8x1.25.

Use a tap to clean the threads and you should be good to go