PROBLEM TO BE SOLVED: To easily and smoothly insert a rod shaft whose outer diameter is approximate to an ear hole diameter into an ear hole of an scallop without bending even if the ear hole diameter is small.SOLUTION: The rod shaft 11 has a plurality of slots 16 in the axial direction on the outer surface, and anti-loosening pieces 12 are cut and raised with a half on one side of each piece in the axial direction of the rod shaft 11 left unraised.