Abstract: A first column-like portion of a hook rod, substantially oval-shape in cross section, is fitted in hooks and then turned around its longitudinal axis by about 90°. Since a diameter in the vertical direction facing to a lower surface of the hook from the center of the first column-like portion having a substantially oval-shape in cross section increases with turning, pressing force becomes larger as the turning angle increases. Therefore, based on the pressing force an upper surface at a flange is pressed toward a flange of a case by a part positioned at the lower end in an outer peripheral surface. Based on the pressing force the flanges, an element peripheral portion sandwiched therebetween is elastically pressed to shrink, whereby the case and the cap are fastened by a simple operation of only fitting and turning the first column-like portion in recesses of the hooks.

Abstract: A first column-like portion of a hook rod, substantially oval-shape in cross section, is fitted in hooks and then turned around its longitudinal axis by about 90°. Since a diameter in the vertical direction facing to a lower surface of the hook from the center of the first column-like portion having a substantially oval-shape in cross section increases with turning, pressing force becomes larger as the turning angle increases. Therefore, based on the pressing force an upper surface at a flange is pressed toward a flange of a case by a part positioned at the lower end in an outer peripheral surface. Based on the pressing force the flanges, an element peripheral portion sandwiched therebetween is elastically pressed to shrink, whereby the case and the cap are fastened by a simple operation of only fitting and turning the first column-like portion in recesses of the hooks.