A retaining cap includes circular projections positioned on the outside of a circumferential surface of a main body of the cap. The projections define a diameter for the cap that is larger than the diameter of the main body of the cap. The retaining cap is joined with the tulip in an assembly by positioning the cap coaxially with the tulip body. The cap is then slid into tulip body with the projections aligned with respective half circle entry slots of tulip body. The cap is the rotated axially to a degree that the tulips diameter is reduced to cause interference between the retaining cap projections and the tulip. The retaining cap can be rotated past the interfering diameter and into a home position created by cross holes in the tulip body where the cap can be removed from the tulip.
