Mitutoyo Holtest Internal Micrometer 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... 0.650" - 0.800" Measuring Range 0.0002" Graduations Features Include... TiN-coated measuring contact points provide excellent durability and impact resistance and allow the instrument to measure right to the bottom of a blind hole. Highly durable because of carbide-tipped contact points (anvils). Measurement can be taken closer to the bottom of the blind bore. Can measure deep holes using an Extension rod (optional). With Ratchet Stop for constant force. Setting Rings for zero point adjustment are optional. Supplied in fitted plastic case.