Useful trivia on ISO metric fasteners and trying to figure out what you might have if unknown.
M6 x 1.00 fastener will be drilled with a 5mm drill then tapped.
M8 x 1.25 fastener will be drilled with a 6.75mm drill then tapped
M8 x 1.5 fastener will be drilled with a 6.5mm drill then tapped
M10 x 1.5 fastener will be drilled with a 8.5mm drill then tapped.
See where this is going?
You can gauge a metric hole (approximately) by the size of drill rod that will just barely fit into the tapped hole. From there you can roughly infer the bolt size and pitch. At which point I'd find that tap and see if it runs in easily. If not, don't force the tap unless you're sure you have the right one or you'll have a complete mess on your hands.
Highly doubtful you have a M7 x any pitch fastener. That would be a very uncommon size for automotive use. If you really think that is the case, check with the crank supplier.
Don't get me started on British machinery and Whitworth fasteners.
Digital calipers and a thread pitch gauge are a must for working on old stuff in my opinion.