| 摘要 |
PROBLEM TO BE SOLVED: To provide an upper shell having no warp and an excellent flatness by forming the area near the internal side of the projected portion at the circumference of the upper shell almost in the same thickness as the external side of the projected portion of circumference. SOLUTION: An upper shell 1 as the projected portion of the circumference projected annually at the center area and the internal circumference area 9 near to the internal side 7 of the projected portion 3 of circumference is formed almost in the same thickness d1 as the external side of the recessed portion 3 of the circumference. Moreover, at the center of projected portion 3 of the circumference, a rectangular abutting part 11 which abbuts against the head portion of rotating shaft is formed thicker than the internal circumference 9 so that it is projected from the internal circumference 9. Thus, at least an area near the internal side of the projected portion of circumference of upper shell is formed in the same or almost same thickness as the external side of the projected portion of the circumference. Therefore, when the upper shell is formed by the injection molding, fluidity of fused resin does not hindered at the external and internal sides of the projected portion of the circumference and the fused resin is smoothly supplied up to the center area of the projected portion of the circumference.
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