If you're building up a Dart block and want the best bearings with the correct sizing, then you'll want Dart cam bearings. They're fully grooved, made from steel-backed babbit, and specifically designed for high performance use. To all of this, Dart adds their own moly-PTFE coating for even better performance and durability. This coating is approximately 0.0005 in. thick, which translates into 0.001 in. less overall clearance.