Measuring some dimensions on parts requires a bit of math (oh, no!). The flange bolt circle is one of them. The bolt circle is defined as the diameter from the center of one bolt hole to the center of the opposing bolt hole. The problem is ... where is the center of a hole?
The work-around is this. Using a pair of calipers:
Need help measuring anything else ... call us at (609) 561-9323 or email Michelle, our flange expert, at firstname.lastname@example.org. We are happy to help.