ball bearing

  1. a bearing in which the moving parts revolve or slide on freely rolling metal balls so that friction is reduced
  2. any of such metal balls

See ball bearing in American Heritage Dictionary 4

noun Abbr. bb
  1. A friction-reducing bearing consisting essentially of a ring-shaped track containing freely revolving hard metal balls against which a rotating shaft or other part turns.
  2. A hard ball used in such a bearing.

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ball bearing

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