or ring section and numeral 22 the intermediate circle indicates the curve of rubber surface as it joins the walls of the band the rubber cover is shown as extending upward over the ball to 20 where it joins the wall 11 of the stud to cover shoulder 13 which is shown in fig1 also it is apparent that the rubber on the lower or flat end 15 of the ball covers this flat end of the ball and normally will be the thinnest on the bottom end where the rubber cover 16 extends from the curved to the flat portion of the metal ball as indicated by numeral 30 in some embodiments it is desirable that the rubber fill the space in fig1 between the flat surface 15 and circle 17 as indicated previously generally the rubber cover is thinnest in the areas indicated by numerals 20 and 30 and the thickest in the area of band 23 where the width of the band 23 is indicated by numeral 24 and its thickness by numeral 29 best seen in fig3 referring again to fig2 it will be noted that the rubber cover 16 has a curve upward from the thinnest sections 20 and 30.