Tool joint with internal/external make-up shoulder

Abstract From the Canadian patent

A tool joint for earth boring drill pipe members has features that increase the amount of torque required to yield the connection. The tool joint has both external and internal make-up shoulders. The pin and box are dimensioned so that the box face contacts the external shoulder while there still is a clearance between the pin face the internal shoulder. At normal make-up torque the external shoulder will be tightened to its normal amount. The internal shoulder will tighten to its yield only if additional torque is encountered while drilling. The internal shoulder adds to the amount of torque required to yield the tool joint connection.