bolt circle

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun engineering A theoretical circle on which the centerpoints of bolt holes lie when the bolt holes are positioned as equally spaced in a circle. Common examples are the bolt circle for the lugs on a car's wheel, or the bolts on a bolted joint between pipe flanges. Often abbreviated "BC" or "B.C." on engineering drawings. Often treated as a basic dimension, when true position for the centers is specified using GD&T.