Patent attributes
A drill rod has a fitting portion protruding toward the distal end of the drill rod. The drill rod fitting portion further encompasses a parallel male thread portion in which a minimum distance from a first axial line in a cross-section perpendicular to the first axial line is constant; and a male thread ending portion is continuous with a proximal end of the parallel male thread portion. The minimum distance of the ending portion increases as a proximal end is approached. Furthermore, the fitting portion is formed such that the minimum distance does not decrease as the proximal end is approached from a distal end thereof. Additionally, the proximal end of the male thread ending portion is positioned where a distance from the first axial line gradually increases as the proximal end of the male thread ending portion is approached from the parallel male thread.
