A constant-velocity joint includes an outer ring having an annular space therein and 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. At least one of the radially outer wall and the radially inner wall has three axially extending track grooves circumferentially spaced apart from each other by 120 degrees. A cage is inserted in the annular space. The cage has pockets at positions corresponding to the track grooves, respectively. A ball is received in each 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 pockets of the cage to prevent the balls from coming out of the pockets of the cage.