| 摘要 |
PROBLEM TO BE SOLVED: To provide a screw hardly letting fracture a soft member used as a female screw member and capable of shortening tact time required for tightening the screw. SOLUTION: This three-streak screw in which a first to a third threads 13, 14, 15 are formed is constituted such that shapes of the second and the third threads 14, 15 are the same and a height h1 of the first thread 13 is larger than a height h2 of the second and the third threads 14, 15. Moreover, a pitch P of each thread is substantially equal to a pitch of an ordinary one-streak thread. Since this is the three-streak screw, it comes into contact with hole fringes in three sections when it bites a female screw hole, thereby preventing the inclination of the screw. Since a lead angle is large, tact time for tightening becomes short, a seating torque can be easily increased hardly to be allowed to loosen. In addition, the female screw member is hardly allowed to fracture.
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