Constant velocity universal joint

A constant velocity universal joint comprising an outer joint element having a bore with a spherical surface and a plurality of grooves in said bore surface, an inner joint element within said bore having a spherical outer surface and having a plurality of grooves in said outer surface corresponding in number to said outer joint element grooves to define pairs of opposed grooves, a plurality of balls between said joint elements with each ball being in a pair of opposed grooves, means between said joint elements for retaining said balls in a plane which bisects the angle between the joint elements, said ball retaining means having a first spherical surface on its outer face and a second spherical surface on its inner face, said bore spherical surface of said outer joint element coacting with said ball retaining means first spherical surface and said inner joint element spherical outer surface coacting with said ball retaining means second spherical surface, the number of grooves in each joint element being divisible by two but being at least four, the center line of each groove lying in a plane spaced from the axis of rotation of the joint element and parallel thereto.