ball bearings

Because the best ball bearings in the early 20th century were made by German manufacturers, ball bearings have usually been sized in millimeters, even those made in the United States–but the balls themselves were frequently sized in inches. The Anti-Friction Bearing Manufacturers Assn. adopted a classification of ball bearings according to their construction, with each type identified by a symbol (such as "BA"). Symbols that include the letter "I" identify types that are nominally sized in inches; of ten types, only two have an "I."

Embedded in the manufacturer's model number for most ball bearings is a three-digit code that gives its dimensions in millimeters. The first digit refers to the series. There are four principal series:

The table below shows the sizes up through a bore of 50 mm, but much bigger sizes are defined. In the medium series, for example, a 356 bearing takes a shaft with a diameter of 280 mm–more than eleven inches.

Designation Bore Series 100
(x = 1)
Series 200
(x = 2)
Series 300
(x = 3)
Series 400
(x = 4)
OD Width OD Width OD Width OD Width
x00 10 26 8 30 9 35 11
x01 12 28 8 32 10 37 12
x02 15 32 9 35 11 42 13
x03 17 35 10 40 12 47 14 62 17
x04 20 42 12 47 14 52 15 72 19
x05 25 47 12 52 15 62 17 80 21
x06 30 55 13 62 16 72 19 90 23
x07 35 62 14 72 17 80 21 100 25
x08 40 68 15 80 18 90 23 110 27
x09 45 75 16 85 19 100 25 120 29
x10 50 80 16 90 20 110 27 130 31
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