An arc guider configured to provide an arc movement path, one side thereof forming a fixation projection and a center thereof forming a groove in a longitudinal direction, a fixation element sequentially including a main contact, an arc contact being spaced apart from the main contact and an insertion groove accommodating the arc guider and a plurality of projection fixing units being formed on both sides of the insertion groove and being curved toward the accommodated arc guider through an outer force so that the fixation projection does not escape wherein triangle V shaped groove marks by the outer force are formed in the plurality of the projection fixing units.