234A-12 Starrett Insulated End Measuring Rod with Spherical Ends: 12"
The Starrett 234A-12 micrometer standard has the following specifications:
Starrett 234A End Measuring Rods or "standards" with insulated handles are for checking and setting micrometers of 2" capacity and larger, and 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.
Starrett 234A Series End Measuring Rods with Spherical Ends:
Starrett S234 Series End Measuring Rods with Spherical Ends Sets: