Rolling body refers to the rolling bearing structure between the inner and outer ring to play rolling friction effect of mechanical parts, because the rolling body is in the bearing work raceway operation, so its own accuracy (such as diameter, roundness, spherical error, etc.) and material characteristics will directly affect the whole bearing running accuracy, affect the bearing clearance, rotational accuracy and other finished indicators and service life.

Rolling body according to its shape and structure in the bearing is divided into: ball, needle roller, cylindrical roller, tapered roller, spherical roller rolling body has precision grading, its precision indicators are generally: diameter, length, shape error, batch changes, etc., all kinds of material indicators are generally similar to the bearing collar.

Measurement methods of various types of rolling elements are clearly defined in the relevant national standards, and the conformity of their indexes (limit value requirements) can be assessed according to the relevant standards or contractual technical agreements at the time of inspection.