Abstract: A threaded fastener is provided in which a head bearing surface can be in full intimate contact with a counterpart. The threaded fastener is provided with a head (10), and a screw shank (20) extending from the head (10). The screw shank (20) is provided with a parallel thread portion (22) having a complete screw thread formed therein, a neck portion (24) having no screw thread, a transition thread portion (26) having an incomplete screw thread formed to extend from the parallel thread portion (22) toward the neck portion (24) with its root diameter being the same as that of the complete screw thread and with its thread height gradually becoming lower to reach the neck portion, and an underneck rounded portion (28) formed in a corner angle portion between the neck portion (24) and a head bearing surface (11), wherein the neck portion (24) is work hardened with its diameter being narrowed from a root diameter of the parallel thread portion (22).

Abstract: A threaded fastener is provided in which a head bearing surface can be in full intimate contact with a counterpart. The threaded fastener is provided with a head (10), and a screw shank (20) extending from the head (10). The screw shank (20) is provided with a parallel thread portion (22) having a complete screw thread formed therein, a neck portion (24) having no screw thread, a transition thread portion (26) having an incomplete screw thread formed to extend from the parallel thread portion (22) toward the neck portion (24) with its root diameter being the same as that of the complete screw thread and with its thread height gradually becoming lower to reach the neck portion, and an underneck rounded portion (28) formed in a corner angle portion between the neck portion (24) and a head bearing surface (11), wherein the neck portion (24) is work hardened with its diameter being narrowed from a root diameter of the parallel thread portion (22).