Inside micrometers and sets are used to measure the inside diameters and internal dimensions of holes, bores, and other openings. 3-point inside micrometers have a gauge head with three contact points that creates a self-centering measurement. Tubular-rod and solid-rod micrometers are used with interchangeable rods to measure a range of small to very large holes. Caliper-jaw micrometers are used to measure smaller bore diameters beneath a groove or lip at the opening of a hole.