US Patent 7361119 Needle bearing and speed reducer using the needle bearing

A radial inner end of a retainer is spaced radially outwardly from a radial outer end of a sliding-contact region, and with this construction the axial movement of each needle roller is limited not by the retainer but by an inner ring, and a restriction flange. Therefore, a large axial force developing in the needle rollers is received by the inner ring and the restriction flange, and as a result, the retainer having low rigidity can be satisfactorily used. Therefore, any suitable material such as a synthetic resin can be selected for the retainer, and besides the wall thickness of the retainer can be made small.