Starrett/$90 - $110
When you need to measure the diameter of a hole, you can either start looking for objects about the same size for comparison or reach for a taper gauge. Aptly named for their tapered shape, the taper gauge measures hole and slot sizes quickly and accurately. This one from Starrett (No. 267) can measure holes and slots from 1/16″ to 1-1/16″—to the nearest 1/64″.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.