This is a one-inch travel micrometer, model number 902R, manufactured by the Millers Falls Company of Greenfield and Millers Falls, Massachusetts. This instrument can measure a dimension to within 1/10,000 of an inch precision. This type of tool was made by the thousands to help the nations World War II (WWII) production effort. It was also used in the Millers Falls Company itself to measure parts like main drill spindle shafts, used in the many power drills that the company made. During WWII, this company supplied the War Department with large quantities of hand tools ( for example bit braces and breast plate drills) and power tools used by the famous Seabees who worked in construction for the armed forces all over the world.