Mechanical caliper-jaw micrometers combine a mechanical vernier scale and thimble actuation with jaws that expand and contract. They are used to measure the inside dimensions of holes, tubes, pipes, or grooves. These micrometers are held at a parallel angle to the surface of a hole or bore to measure the diameter of the bore or to take measurements beneath a groove or lip at the opening of a hole. Users adjust the thimble to contract or expand the jaws until they make contact with the sides of the hole. The operator reads the measurement from the main and vernier scale. Mechanical micrometers do not require batteries.