and at the same height as the first protruding portion 513 in the illustrated embodiment the fastener 53 is a screw and the length of the fastener 53 is longer than the through hole 5111 the pivoting component 55 is a rod to fit the pivoting holes 5123 each of the connecting rod assemblies 70 includes a cam 71 and a rod 73 fixed on the cam 71 the cam 71 defines a pivoting hole 711 to align with the pivoting hole 5123 and there is a resisting end 713 on the end of the cam 71 the distance between the pivoting hole 711 and the resisting end 713 is longer than the distance between the pivoting hole 711 and the surface of the latching portion 114 in assembly first the latching member 38 is fixed on the end of the body 311 parallel to the resisting plate 313 and the stopping strip 39 is fixed on a side of the body 311 perpendicular to the resisting plate 313 thus the body 311 the resisting plate 313 the latching member 38 and the stopping strip 39 cooperatively define the latching space 315 second the elastic member 35 is sleeved on fixing portion 371 and the resisting surface 3731 abuts.