Measures the Inner Diameter of the cylinder bores during the reconditioning process.  This gauge ensures that our cylinder bores are within spec to one tenth-thousandth of an inch. (0.0001").  This is crucial in engine rebuilding as this measures the warp and roundness of the cylinders.    We can measure for taper, wear, depth of a scratch, barrel shape, and the ring wear step at top of a cylinder.   This simple gauge can be set to spec, and then will show +/- the gauge reading.    Very useful gauge to have in the engine machine shop.