Measuring Carrillo rod bolt stretch requires a tapered micrometer. The anvil and shaft are tapered to center up in the holes on each end of the Carrillo bolts. Standard flat faced micrometers will not center up and give false readings. Measuring the stretch accurately is absolutely critical. Uneven or inaccurate measurement of stretch can cause out of round conditions and contribute to bearing failure.

Pricing in tool catalogs can range up to $500 for a tapered micrometer. This economy version will last forever and every serious engine builder should have one.