main body slider 24 the other ends are into plural cylindrical recesses of the spring receiver 28 the coil springs 25 are sandwiched between the main body slider 24 and the spring receiver 28 the main body slider 24 and the spring receiver 28 are slidable in one direction by the guide walls 27 a and 27 b of the case half bodies 15 a and 15 b a pin p 5 for restricting sliding of the spring receiver 28 is provided to run between the paired case half bodies 15 a and 15 b in the spring receiver 28 a long hole 28 a is formed for insertion of the pin p 5 by the coil spring 25 the spring receiver 28 is acted upon by a biasing force in the right and back direction in the figure sliding in the right and back direction of the spring receiver 28 is restricted by the pin p 5 here the main body slider 24 and the spring receiver 28 take identical shapes this is because a single die is used in injection molding of both of the main body slider 24 and the spring receiver 28 at an end of the main body slider 24 a mountain shaped projection 24 a is formed in this projection 24 a a recess 24 b and a long hole 24 c are formed as two pin receivers corresponding to the two pins.