Fowler 53-646-000-1 Bore Gage Setting Master Kit features a 36 piece gage block set. Accurately sets most bore gages up to 6 inches in diameter to an accuracy of .0001". With a quick-release holder for fast adjustment and the economy gage block set has tolerances up to ± .00005" with a certificate of calibration to NIST. Comes in a high-quality aluminum case with a 1-year warranty offered by Fowler precision. Bore gages have a two- or three-point contact, indicating how many points on the gage head touch the inside of the bore. Two-point contacts are better at measuring ovality, while three-point contacts are used to measure lobing or triangular form error. Pistol-grip bore gages are used for fast, single-handed operation with repeatable results from one operator to another. Bore gages can also be used in special applications, such as measuring threads, spline pitch diameters, and deep bores. Fowler, an American company, manufactures premium inspection and measurement instruments like electronic indicators, calipers, bore gages, and micrometers. The company, founded in 1946, is headquartered in Canton, MA.