The Starrett 224 series interchangeable anvil micrometer includes a set of interchangeable anvils to provide a full range of measurement in steps of 1. It has a vernier scale in inch units for taking precise outside diameter (OD) measurements, and a ratchet-stop mechanism that helps provide uniform pressure for precise, repeatable measurements. The micrometers frame is made of ribbed cast iron with perforations that helps provide light weight with rigidity. The vernier scale on the thimble and sleeve is graduated to 0.001, with a satin chrome finish that helps resist rust and reduce glare. The spindle and anvil are made of hardened steel for durability. A knurled ring-type lock nut helps provide secure locking of the measurement position. The micrometer and accessories come with a fitted wood 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.The L.S. Starrett Company manufactures precision measuring tools, metrology and testing equipment, and saw blade products. The company was founded in 1880 and is headquartered in Athol, MA.