A typical set of "small hole gages", together with a Mic or caliper will provide a decent measurement of a bore
Mike
Mike
This method doesn't work out with an odd number of grooves.
As you likely know, the small hole gage takes a dimension across two points at 180 degrees from each other - and with am odd number of grooves that dimension would be land-to-groove, not land-to-land or groove-to-groove.
Taking a measurement of the bore diameter with pin gages (which will get you very close to that number), then measuring with a small hole gage can get you very close to the actual groove diameter but it will take a bit of math to get you there.