shaft portion 136 of lower mandrel tool body 140 substantially in alignment with longitudinal bore 130 of bar string 7 thereby allowing the flow of test fluid therethrough lower fluid flow passage 150 corresponds to upper fluid flow passage 98 of piston portion 92 of upper mandrel tool body 90 sufficient background has now been afforded for a description of the improvements of this invention over the prior art the improvements are as follows a a transverse bore 192 or lower filling jet 192 provided through bottom portion 138 of piston portion 144 of lower mandrel tool body 140 lower filling jet 192 communicating with lower fluid flow passage 150 and a transverse bore 83 or upper filling jet 83 through the topmost portion 94 of piston portion 92 of upper mandrel tool body 90 upper filling jet 83 communicating with upper fluid flow passage 98 b upper filling jet 83 and lower filling jet 192 as above described except that upper filling jet 83 and lower filling jet 192 are disposed at an approximately 45 u00b0 angle to upper fluid flow passage 98 and lower fluid flow passage 150 respectively d o rings 110 111 mounted to the machine threaded part of the shaft portion 106 of upper mandrel tool body 90 the prior art teaches of filling jets which are provided in the shaft portion rather than the piston portion of the mandrel tool bodies this dispositon of filling jets causes a weakening of the shaft portion of.