Originally Posted by randle_ford
How do I figure out what size Heli-Coil to use? The bolt is 10mm (not sure of the thread count)
You mean 10mm head with a 6mm thread? If you go and ask for a 10mm bolt they'll come back with one about as big around as a cigarette. It's measured by thread diameter, not fastener diameter.
Personally I would just get a 7mm tap and bolt. A lot less metal is taken out of the casting that way and it will hold just fine.