The S234MC Standards Set is designed for checking and setting Starrett S436.1M and S436M Micrometer sets with 0-75mm range. These End Measuring Rods or "Standards" are also used on machine tools for comparing gages, checking precision measuring tools, for measuring parallel surfaces, and many other types of work. They are made of special tool steel in rod form with ends hardened and accurately lapped to a spherical radius. Rods or Standards are for checking and setting micrometers of 50mm to 75mm capacity