A tab main body section (520) is provided with first to third main body section slits (731-733) which penetrate through the tab main body section (520). The first to third main body section slits (731-733) are formed in a circular arc shape so as to extend along the outer peripheral edge of an insertion hole (540) formed in a circular shape. The first main body section slit (731) is provided between the insertion opening (540) and a first edge section (501) of a tab (500). The second main body section slit (732) and the third main body section slit (733) each have one end section (751) and the other end section (752). The one end section (751) is located closer to a second edge section (502) of the tab (500) than the insertion hole (540).