Coaxial Indicator
A coaxial indicator is one variety of indicator used to measure the center of bores, shafts, arbors, holes, and more. When clamped into a tool holder, like a mill, the coaxial indicator is positioned at the center of the axes across the hole and the tip of a probe is adjusted to touch the surface around with the tool is being centered. Once on, the movement of the probe is translated into the measurement on the dial gauge. Coaxial indicators are versatile tools that come with a selection of inside, outside, straight, and bent probes, making them perfect for accurately measuring the center of a number of parts.