External screw member

A external screw member comprising a head, and a shank extending linearly from said head, said shank having a parallel threaded portion and a tapered threaded portion formed in order from said head toward a tip end, a screw thread being continuously formed on said parallel threaded portion and said tapered threaded portion at the same pitch, and said screw thread in said tapered threaded portion being configured in a form in which the height of a crest thereof becomes gradually smaller, wherein

• a convex portion protruding more radially outward than the crest of said screw thread is formed in at least one of said parallel threaded portion and said tapered threaded portion over said tapered threaded portion and said parallel threaded portion;
• a screw driving side end face of said convex portion is configured to form an inclined plane which gradually rises from a root position of said end face at the side of the crest of said screw thread toward a crest of said convex portion in a direction opposite to a screw driving direction of said screw thread to reach the crest of said convex portion;
• and
• a pressure side flank of the screw thread having said convex portion is configured such that it is composed of at least two or more flank portions with different flank angles, and that it has one or more points of inflexion which each become a boundary of each of said flank portions, and that a flank angle of a root side flank portion adjacent to a first point of inflexion is larger than a flank angle of a flank portion at the side of the crest, with said first point of inflexion located at the side closest to the crest as a border;
• the flank portion at the side of the crest inclines linearly from the crest of the convex portion;
• and
• a corner is provided between the crest side flank portion and a convex crest.

An external screw member comprising a head, and a shank extending linearly from said head, said shank having a parallel threaded portion and a tapered threaded portion formed in order from said head toward a tip end, a screw thread being continuously formed on said parallel threaded portion and said tapered threaded portion at the same pitch, and said screw thread in said tapered threaded portion being configured in a form in which the height of a crest thereof becomes gradually smaller, wherein

• a convex portion protruding more radially outward than the crest of said screw thread is formed in at least one of said parallel threaded portion and said tapered threaded portion over said tapered threaded portion and said parallel threaded portion;
• a screw driving side end face of said convex portion is configured to form an inclined plane which gradually rises from a root position of said end face at the side of the crest of said screw thread toward a crest of said convex portion in a direction opposite to a screw driving direction of said screw thread to reach the crest of said convex portion;
• and
• a pressure side flank of the screw thread having said convex portion is configured such that it is composed of at least two or more flank portions with different flank angles, and that it has one or more points of inflexion which each become a boundary of each of said flank portions, and that a flank angle of a root side flank portion adjacent to a first point of inflexion is larger than a flank angle of a flank portion at the side of the crest, with said first point of inflexion located at the side closest to the crest as a border;
• wherein a second point of inflexion is formed closer to a root side of an external thread than said first point of inflexion, and is formed of an intermediate flank portion having an angle still larger than that of said root side flank portion, and the flank angle of said intermediate flank portion is set to be larger than the flank angle of the root side flank portion, and the flank angle of said root side flank portion is set to be equal to or more than a flank angle of a crest side flank portion.