| 摘要 |
An engagement protrusion (20) extending in the front/back direction of a frame body (13) is provided on one of the opposing surfaces of a notch (16) in the frame body (13) and a fitting member (17) opposite said notch; similarly, an engagement recess (13h) in which the engagement protrusion (20) fits is provided on the other of said surfaces. By means of the moment of the fitting member (17) resulting from the tension of a tension member (14), the engagement protrusion (20) and the engagement recess (13h) are prevented from separating. |
