cut surface 112 of fig2 a is continuous with the same cut surface 112 of fig2 b axial flow passage 114 extends longitudinally i e axially downward from the upper portion 108 of upper connector 104 through the upper connector and into a generally tubular seal sub 116 seal sub 116 has three longitudinally spaced apart circumferential seals 118 disposed thereon which sealingly engage the upper connector 104 from the seal sub 116 the axial flow passage 114 extends axially downward through a tubular inner mandrel 120 inner mandrel 120 is sealingly and threadedly attached to the seal sub 116 at an upper end 122 of the inner mandrel at a lower end 124 of the inner mandrel 120 the inner mandrel is sealingly and threadedly attached to an upper portion 128 of a generally tubular connector 126 the axial flow passage 114 extends axially through the tubular connector 126 and into a crossover 132 which is sealingly and threadedly attached to a lower portion 130 of the tubular connector the axial flow passage 114 terminates at upper radially reduced portion 134 of generally cylindrical plug 136 plug 136 is threadedly installed into lower portion 138 of crossover 132 and secured with a pair of set screws 140 only one of which is visible in fig2.