There are three most basic categorizations of micrometers. Those types are inside, outside, and depth micrometers. The reason that these are known as the most basic types is that the majority of the measurements you may need to complete can be accomplished with these tools. An inside micrometer is used to measure the internal dimensions of an object, an outside micrometer is used to measure the external dimension of an object, and a depth micrometer is used to measure the depth of a hole. In fact, the outside micrometer is one of the most widely used precision measurement tools overall. These versatile micrometers are excellent devices to have on hand no matter what specific type of metrology you do.