COUPLINGS FOR ROTARY DRILL STRINGS
Male and female coupling members (120, 130) for a drill string (10) have abutment faces (122, 132), fitted with torque reducing rings (124, 135) of low-friction, material, and multi-start threads (140, 150), with higher lead angles PROPORTIONAL than forconvention coupling threads, to enable uncoupling of the coupling members (120, 130) at reduced torque.