Constant-velocity joint and image-forming device

摘要

A constant-velocity joint includes an outer ring formed with an annular space therein having an opening at one axial end thereof. The annular space is defined by a radially outer wall and a radially inner wall of the outer ring. One of the radially outer wall and the radially inner wall is formed with three axially extending track grooves circumferentially spaced apart from each other by 120 degrees. A cage is inserted in the annular space and formed with pockets at positions corresponding to the respective track grooves. Balls are each received in one of the pockets so as to roll along one of the track grooves. A pair of diametrically opposed protrusions is formed at radially inner and outer open ends of the respective pockets of the cage to prevent the balls from coming out of the respective pockets of the cage.