The Starrett 222 series sheet metal micrometer has a deep-throated frame for measuring thickness of sheet metal, paper, plastic, or rubber parts, a vernier scale in inch units for taking precise outside diameter (OD) measurements, and a ratchet-stop mechanism for uniform pressure during adjustment. The micrometer frame has a black wrinkle finish that helps resist rust. The vernier scale on the thimble and sleeve is graduated to 0.001, and has a satin chrome rust- and glare-resistant finish. The spindle and anvil have micro-lapped measuring faces for accuracy and are carbide-tipped for wear resistance.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.