Abstract: The problem of seals not functioning properly with known service tapping tools can be solved through the use of interfitting yokes and fasteners holding these yokes in securing such tools relative to couplings on branch or service lines. Such tapping tools are constructed so as to each include a plug structure adapted to internally fit in sealed relationship within the interior of a branch line and/or coupling on the same, a boring bar mounted on the plug structure so as to extend through the plug structure and so as to be linearly and rotatably mounted with respect to the plug structure, an appropriate cutting tool held by the boring bar, and a mechanism for holding the plug relative to the branch line, such mechanism normally being constructed so as to engage the coupling on the branch line. When a yoke and fastener structure as referred to in the preceding is used the plug structure is held so that it cannot cock in such a manner as to affect the sealing at the exterior of the plug structure.