Inspection ball kits are available from stock in the 14 most popular English sizes from 3/32" to 1.00", individually or all in a kit. Each individual group of balls contain a nominal fractional ball as well as one each of a +.002", +001", +0005", +0002", and -.001", -002". The inspection ball kits are also excellent for ball sizing parts. Ball sizing is basically pushing a ball through a hole or tube which produces a certain finish or size.
The balls are precision lapped to meet the A.F.B.M.A. standard Grade 25. They are spherical within 25 millionths of an inch (635 nm). The surface finish is below 1.5 micro inches (38.1 nm) Ra and the exact ball size is within + or - .0001" of an inch (.00254 mm).
The balls are manufactured from chrome alloy steel that is hardened to 62 Rockwell C for wear resistance. This material has a thermal coefficient of expansion equal to 6.3 micro inches per inch per degree Fahrenheit or 11.4 micro meters per meter Centigrade. This matches steel gage blocks and is the same as most iron and steel products.
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