Mitutoyo Holtest II Internal Micrometer Set These Holtests are versatile, self-centering three-point internal micrometers for the accurate and efficient direct-measurement of internal diameters. Three anvils, evenly spaced at 120° apart, contact the internal wall surfaces and find true alignment with the axis of the bore for accurate ID measurement. Specifications Include... 4.0" - 8.0" Measuring Range 0.0002" Graduations +0.00025" Accuracy Set includes... 4.0" - 5.0" Range Holtest 5.0" - 6.0" Range Holtest 6.0" - 7.0" Range Holtest 7.0" - 8.0" Range Holtest 5" Inner Diameter Setting Ring 7" Inner Diameter Setting Ring Extension Rod Wood Case Features Include... Hardened Steel Measuring Contact Points provide excellent durability allow the instrument to measure close to the bottom of a blind hole. Measurement can be taken closer to the bottom of the blind bore. Can measure deep holes using an Extension rod (included). With Ratchet Stop for constant force.