Coupling for rotary drill strings

A coupling assembly for a rotary drill string including:

• a male coupling assembly or pin, and a complementary female coupling member, or box, operable to couple together adjacent components of the rotary drill string;
• the male coupling member having a body with a divergent, screw-threaded distal portion, terminated by an annular abutment face;
• the female coupling member, or box, having a convergent, internally screw-threaded bore, or socket, where a distal end of the female coupling member is terminated by an annular abutment face operable to engage the annular abutment face about the male coupling member;
• wherein:
• a ring or annular body, having a lower co-efficient of friction, is interposed, or placed between, the annular abutment faces of the male and female coupling members to reduce the torque required to uncouple the coupling assembly.