Bore gages and ID gages are designed for dimensional measurement or assessment of the internal diameter of components.  Bore gages and ID gages are available that employ mechanical or electronic readout

Indicating bore gages are gaging devices for comparative measurements where the linear movement of a spindle or plunger is amplified and displayed on a dial, column or digital display.

3-point bore gages have three contact points mounted on arms that expand out from a central point.  3-point bore gages can detect lobe or out-of-roundness conditions, which is an advantage over 2-point ID gages.  These gages can have either a dial bore indicator or a digital display.