Ball (bearing)

[2] Bearing balls are manufactured to a specific grade, which defines its geometric tolerances.

[3][4] Lower grades also have fewer defects, such as flats, pits, soft spots, and cuts.

[4] This is measured by rotating a ball against a linear transducer with a gauge force of less than 4 grams (0.14 oz).

The wire is sheared to give a pellet with a volume approximately that of the ball with the desired outer diameter (OD).

[6] Sometimes the balls are then run through a soft grinding process afterward to improve precision.

They are ground in the same type of machine as used before, but either an abrasive is introduced into the coolant or the rotating plate is replaced with a very hard fine-grain grinding wheel.

[5] The inspection of bearing balls was one of the case studies in Frederick Winslow Taylor's classic Principles of Scientific Management.

[6] Ceramic bearing balls are made of sintered materials that are then ground to size and shape as above.

Common materials include: silicon nitride (Si3N4) and zirconium dioxide (ZrO2).

Other less common materials include copper, monel, k-monel, lead, silver, glass, and niobium.