SPI Electronic Internal 3-Point Micrometer Set Specifications include... 2.00" - 4.00" Measuring Range 0.00005" / 0.001mm Resolution + 0.00020" Accuracy 4.49" Measuring Depth 0.020" Contact Point Length Complete Set includes... 2.0" - 2.5" Measuring Gage 2.5" - 3.0" Measuring Gage 3.0" - 3.5" Measuring Gage 3.5" - 4.0" Measuring Gage 2 Setting Rings 6" Depth Extension Short Form Certificate of Calibration Features include... Self Centering 3 contacts points for accurate measurement of internal diameters. Measurement can be taken close to the bottom of a blond bore, can also be taken in a deep bore with extension rod. Inc./abs./inch/metric measuring Carbide tipped contact points. Supplied with setting ring and extension rod Protection level IP54 Ratchet thimble Certificate of Calibration . Furnished in fitted aluminum attache.