SCREW HAVING MULTIPLE-THREAD NECK LOWER SCREW PART

摘要

To improve bolts in conventional art, especially enhance safety in use, and increase holding force in an installed state.SOLUTION: A bolt (10) comprises a head part (11) with an action part for tool, a shaft part (18) with at least one first screw portion (13) and second screw portion (15), and a tip part (16). The first screw portion (13) is a neck lower screw part continuing to a neck portion (12) having no thread. The neck lower screw part (13) is designed as a screw with at least two threads. It is necessary that a pitch of the first screw portion (13) is longer than a pitch of a second screw portion (15), and an axial path difference over the whole screw length of the first screw portion is 3.5 mm at a maximum.SELECTED DRAWING: Figure 5