The Starrett 128 Inside Micrometer Set consists of a satin-chrome micrometer head which can be used in combination with any one or more of a series of rigid, tubular steel measuring rods to obtain the required length. With (1) 4-6 Head, (1) each 2, 4, 6, 8, 10, 12 Rods, (1) 12 Ext., (2) 24 Ext. 6-78 Range, .001 Grad with Finished Case.