A dial indicator is a precision instrument; anyone who’s got one of these suckers in their tool set means business.
That’s because a dial indicator is used to measure very slight imperfections in endplay, runout and backlash. Just knowing what these words mean will make you look like a pro, but being able to use one of these suckers? Please, your friends will start calling you for car advice.
Endplay is axial movement in a shaft; you might, for example, place the dial indicator against an engine’s flywheel, and push the crankshaft fore and aft— the tip of the dial indicator will plunge, and the dial will tell you how much the shaft has moved— that’s called endplay.
Runout measures roundness of a shaft, and can help you identify strange vibrations in your drivetrain. And backlash is the amount of play in a gear mesh— an important parameter when doing work with differentials or transmissions.
So yes, a dial indicator is a bit specialty tool, but considering how many rotating components and gear meshes there are in a car, these things can come in very handy. Plus, it measures in thousandths of an inch— nothing like some precise instruments to make you seem like you know what you’re doing.