Fowler 54367020BT XTD3 .375"-.750"/10-20mm measuring range Bluetooth electronic Holemike set has 3-point heads, 0.00005"/0.001mm graduation, 0.00015"/0.004 accuracy, up to 2.44"/62mm depth & comes with full 5 year warranty. Features tungsten carbide measuring face & blind bore capability. This digital inside micrometer has a ratchet stop for consistent measuring and non-removable anvils. This Holemike has 4 preset memories, larger easy-to-read display, direct inch/metric conversion, proximity & Bluetooth connectivity. It comes with 3 heads, 1 handle, 2 setting rings and UKAS certificate for micrometer, heads and setting rings, special anvils available upon request. The Fowler/Bowers XT3 Digital Internal Micrometers have been designed to further simplify the accurate measurement of bores. All XT instruments offer fixed anvils. Sizes above 1"/25mm offer extended travel. Bore gauges measure holes, or bores, in a workpiece. Internal micrometers can only measure to the depth of their teeth while bore gauges allow more depth range. Bore gauges are typically calibrated with a setting ring & come in 2 types: simple & direct-measuring. Simple bore gauges are used with a caliper to transfer the hole measurement, while the more complex gauges take the measurement directly, & display it through a Vernier, dial, or digital display. Two-point contact bore gages are better at measuring ovality, while three-point contacts are used to measure lobbing or triangular form error. Pistol-grip bore gauges are used for fast, single-handed operation with repeatable results from one operator to another. Bore gauges can also be used in special applications, such as measuring threads, spline pitch diameters & deep bores.