plug 1 the proximal end of the push rod includes a centering post 171 and a radially extending surface 173 for pushing against the expander member 19 push back mandrel 161 can be used for both pushing the expander member 19 out of position in the plug 1 and also for pulling a plug 1 however because the push back mandrel 161 is not a solid member and may break or deform due to the stresses applied and by the tool 31 it is generally preferable to use a solid mandrel 37 such as those illustrated in fig8 and 9 for plug pulling to remove a plug a push back mandrel 161 having a push rod member 165 is first secured to the pneumatic cylinder 35 the tool 31 is positioned directly beneath a plug 1 using visual aids and leveling devices not shown and the push back mandrel is screwed into the plug 1 by turning the pneumatic cylinder 35 at this stage the push rod 165 is in a lowered position see fig3 a and the chamber 43 is not pressurized until the push back mandrel 161 is rigidly secured to both the plug 1 and the pneumatic.