shown in fig4 and 5 of the drawings each of the spacer rings or thrust washers 54 and 56 only one being shown for the sake of brevity includes a plurality of shallow arcuate grooves 166 in each end face to provide for lubricant flow around the spacer rings when the joint is fully assembled fig1 the grooves 166 are equispaced at 120 u00b0 and the grooves on one side of the ring are offset by 60 u00b0 with respect to the grooves on the other side it is preferred that the spacer rings 54 and 56 be made from a powdered metal which is impregnated with a bonded lubricant for example the rings 54 and 56 are formed from a powdered metal designated by the international hough code fn 0205 s which is based on the metal powder industries federation mpif system the codes are based on chemistry and are further classified by density using suffix letters the prefix letters indicate alloy type the four digit numbers indicate the amounts of major alloy element and carbon the suffix letter indicates the density range the powdered metal fn 0205 s has an approximate astm code number b464 grade 1 class b and type.