The Mitutoyo 139 series tubular vernier inside micrometer has a vernier scale in inch units for taking precise inside dimension (ID) measurements of the inside dimensions of cylinders, rings, and parallel surfaces. It may also be used with interchangeable extension pipes for a diversified range of measurement (sold separately). The vernier scale is graudated to 0.001”, and has a satin chrome rust- and glare-resistant finish. The micrometer head has a travel of 0.5” or 1” per revolution depending on the model. A knurled ring-type lock nut helps hold measurements in place. The micrometer and accessories come with a wooden case for storage.Micrometers are precision measuring instruments that use a calibrated screw to measure small distances. These measurements are translated into large rotations of the screw that are then able to be read from a scale or a dial. Micrometers are typically used in manufacturing, machining, and mechanical engineering. There are three types of micrometer: outside, inside, and depth. Outside micrometers may also be called micrometer calipers, and are used to measure the length, width, or outside diameter of an object. Inside micrometers are typically used to measure interior diameter, as in a hole. Depth micrometers measure the height, or depth, of any shape that has a step, groove, or slot.Mitutoyo manufactures precision measuring tools, metrology equipment, and systems. The company was founded in Tokyo in 1934 and formed Mitutoyo America Corporation in 1963, which is headquartered in Aurora, IL.