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) 100-150mm Head, (1) ea. 50, 100, 150, 200, 250, 300mm Rods, (1) 300mm Ext., (2) 600mm Ext. 150-3750mm, 0.01mm Grad with Finished Case Ext.