a pair of less deformable elongated plate shape bodies, each of which has a pinching portion at one end with a flat pinching surface on an inner surface, a supporting portion at other end with a flat contact surface on an inner surface, a handling portion between the one end and the other end with an inner surface;

a resilient body which couples the pair of the plate shape bodies to be spring-loaded in a direction of separation of the two plate shape bodies; and

wherein, when the pinching surface and the contact surface of one of the plate shape bodies is brought into contact with those of the other of the plate shape bodies, the pinching surfaces and the contact surfaces are respectively tightly in contact with each other, and the resilient body is fitted to the support portions.