Roof bit coupling

In a mine roof drilling system of the type having a drive member and a bit member, a high torque coupling for releasably interconnecting said members for rotation about a common axis, said coupling including:

• a plug on one of said members projecting axially from an end thereof and having an outermost axial-locking segment and a discrete torque-transmitting segment;
• a socket in one end of the other said members adapted to releasably receive said plug with said members axially aligned;
• and
• a radial constriction in said socket, said constriction having an acircular transverse cross-section;
• said axial-locking segment having a transverse cross-section complemental to said acircular cross-section of the constriction to permit the axial-locking segment to pass through the restriction when the cross-sections are aligned for insertion or withdrawal of the plug from the socket;
• said torque-transmitting segment having an acircular transverse cross-section dissimilar to the cross-section of said restriction and cooperable therewith to permit limit relative rotation of said members with respect to one another between right- and left-hand torque-transmitting positions when the plug is received within the socket;
• said axial-locking segment being angularly positioned about the axis of said one member relative to said torque-transmitting member such that the locking-segment is angularly misaligned with said restriction when the members are in one of said torque-transmitting positions whereby to preclude withdrawal of the plug from the socket by solely axial movement.