Abstract: An extendable shaft includes: an inner shaft including a plurality of external teeth; an outer shaft including a plurality of internal teeth that slides relatively to the external teeth; and a resin layer covering the external teeth. The pressure angle of the external teeth is different from the pressure angle of the internal teeth.

Abstract: A method for manufacturing a spline telescopic shaft according to the present disclosure includes a toothless portion forming step of forming a toothless portion in one of an external tooth of a shaft body and an internal tooth of a tubular body, a resin layer forming step of forming a resin layer by arranging one of the shaft body and the tubular body in a mold including a cavity and injecting a resin into the cavity, the cavity being included in a flat receiving surface that faces tooth flanks of one of the external tooth of the shaft body and the internal tooth of the tubular body, and a cooling step of cooling one of the shaft body including the resin layer and the tubular body including the resin layer to form a lubricant reservoir in the resin layer.

Abstract: A telescopic shaft includes an inner shaft and a cylindrical outer shaft that are fitted together. A first raceway groove extending in the axial direction is formed in an outer peripheral surface of the inner shaft. A second raceway groove extending in the axial direction and facing the first raceway groove is formed in an inner peripheral surface of the outer shaft. A plurality of balls interposed between the first and second raceway grooves and arranged in a row in the axial direction roll in a first stroke range in the axial direction with respect to the inner shaft and roll in a second stroke range in the axial direction with respect to the outer shaft as the inner and outer shafts move relative to each other in the axial direction. The depth of the first raceway groove decreases from the middle toward both ends of the first stroke range.

Abstract: A universal joint includes: a pair of yokes each including a pair of arms in each of which a bearing hole is formed; four bearings each including a bearing cup press-fitted into the bearing hole and a plurality of needle rollers; and a joint spider including four shafts respectively supported by the bearings. A clinched portion that hinders the bearing cup from slipping out of the bearing hole is formed at the peripheral edge of the bearing hole. In the universal joint, the clinching amount for forming the clinched portion is set in accordance with a radial clearance, which is formed between the shaft of the joint spider and the needle rollers, to adjust the size of the radial clearance.