a high performance constant velocity universal joint is based on a body which encloses the constant velocity joint components and provides a smooth spherical outer surface . a one - piece semi - rigid plastic boot in the form of a truncated sphere has a smooth internal spherical surface sized to match the outer surface of the body . the plastic of the boot is sufficiently elastic to allow the boot to snap over the body , yet sufficiently resilient to snap the open end closed after the boot is snapped over the body to provide a substantial seal preventing entry of debris under the seal . a retaining ring is positioned on the boot near the truncated end to resist plastic creep which would result in enlarging the opening and allowing debris to enter the seal .