US Patent 8136846 Cylindrical tapered thread form for tubular connections

A thread form is shown which is used to make a threaded connection between two tubular members and which is capable of being screwed together and subsequently unscrewed. A pin member is provided having external threads with stab flanks and load flanks and flat crests and roots for mating with the mating internal threads of a box member to make up a pipe connection. The thread crests on the pin member are cylindrical with respect to a central longitudinal axis of the tubular member while the thread roots are cut on a taper so that the height of the threads vary over the length of the thread form. The threads on the pin and box members can also be cut oppositely so that respective members of the thread forms are mirror images of each other.