Patent ID: 8061946

Claim:
A pair of threaded members comprising: an internally threaded member and an externally threaded member, wherein the internally threaded member includes a thread formed on an internal surface thereof having a continuous uniform profile, an internal crest and an internal root, and wherein the external threaded member includes a thread formed on an external surface thereof having a continuous, uniform profile, an external crest and an external root; a pair of flanks, which extend in a straight line between the internal root and the internal crest on opposite sides of the internal thread, respectively, when viewed in a cross-sectional plane of the internally threaded member, and a pair of flanks, which extend in a straight line between the external root and the external crest on opposite sides of the external thread, respectively, when viewed in a cross-sectional plane of the externally threaded member, wherein, with the internally threaded member and the externally threaded member screwed to each other, a pitch diameter is defined as the diameter of an imaginary cylinder where the thickness of the thread equals the gap between adjacent turns of the thread as viewed in the traverse direction, wherein the imaginary cylinder is coaxial with the internally threaded member and the externally threaded member, and wherein the pitch diameter of the internally threaded member is substantially the same as the pitch diameter of the externally threaded member, engaging surfaces of the flanks of the internally threaded member face and engage corresponding surfaces of the flanks of the externally threaded member, respectively, each engaging surface has an inner engaging portion, which extends from the internal root to the pitch diameter and an outer engaging portion, which extends from the pitch diameter to the internal crest, as measured in the cross-sectional plane of the internally threaded member, and a length of each inner engaging portion is less than a length of each outer engaging portion, as measured in the cross-sectional plane of the internally threaded member.