Extensions can be added to both the 780XT and 78XT Series, enabling internal measurements in deep hole bores. (Multiple extensions can also be used.). 4" Length.
Internal Micrometer Extension, 1/2-3/4" (12.5-20mm), 4". The Starrett Internal Extensions for 78 Series Internal Micrometers includes 1/2-3/4" (12.5-20mm) sizes, 4" extension size, and fits modeles 78XT/780XT/781XT625-750. Extension 4"/100mm Long for use with 78/780/782, 500-750.