direction from the annular groove 133 for making a communication between the annular groove 133 and the two through holes 137 among the four through holes 137 which two holes 137 have been diametrically spaced apart in the horizontal direction in fig6 the member 120 has a pair of through holes 127 which are diametrically spaced away located in the horizontal direction in fig6 penetrating therethrough in the upper face 121 of the member 120 communicating channels 28 have been formed extending in the radial direction from the annular groove 123 for providing communication between the annular groove 123 formed in the upper face 121 and the opening ends of the remaining two through holes 137 of the four through holes 137 in the side of the lower face 132 which remaining two holes 137 have been diametrically spaced apart in the vertical direction in fig6 in the upper face 111 of the member 110 communicating channels 118 have been formed extending in the radial direction from the annular groove 113 for communicating with the two through holes 127 opened on the lower face 122 of the member 120 said two holes spaced away in the horizontal direction in fig6 the members 110 120 130 and 140 that have been.