Ball screw

A ball screw comprising:

• a screw shaft provided with a helical ball rolling groove having a predetermined lead angle,
• a nut member having a through hole through which the screw shaft is passed, and a helical loaded rolling groove formed in an inner circumferential surface of the through hole, opposed to the ball rolling groove and engaged with the screw shaft via plural balls rolling in the ball rolling groove and loaded rolling groove,
• a pair of ball passing holes formed between an outer circumferential surface of the nut member and the inner circumferential surface of the through hole, each of which is joined to opposed side portions of the loaded rolling groove, and
• a return pipe having a pair of leg portions inserted into relative pair of ball passing holes, and fixed to the nut member so as to form an endless ball circulating passage,
• wherein an axis of the ball passing holes are formed so as to incline from cross sections thereof which are perpendicular to an axis of the screw shaft in an axial direction of the screw shaft by an angle equal to a lead angle of the ball rolling groove of the screw shaft, and
• the return pipe has at least a pair of return pieces, one of the return pieces including one of said leg portions which is inserted into one of the ball passing holes in a direction inclined at an angle equal to the lead angle and fitted in the ball passing holes without causing a clearance to occur therebetween.