I use a micrometer and caliper (Dial) regularly at my shop as well as indicators and other measuring equipment and it has made my bike work much easier. I have been grinding custom cutting tools for 45 years and for me proper measuring tools are as useful as a good set of wrenches! No more guessing? I would say for the average bike mechanic the most useful measuring tool would be dial or digital calipers. The digital ones are nice as you can use them in metric mode or SAE. Also they not only measure O.D. but I.D. and depth . Joe