outer race 9, a cage 11 for retaining the circumferential spacing of the rolling elements 10 and seals 12 and 13 fixedly attached to the outer race 9 and rubbing on a cylindrical bearing surface of the inner race 8, placed on one side and the other of the row of rolling elements 10 to prevent foreign elements from intruding close to the rolling elements 10 and to retain a lubricant such as grease