According to the above embodiment, the flanged bosses respectively have a body portion and a flange portion formed around a free end of the body portion and the quick-release guide rails respectively have a rail portion and a quick-release hole portion communicable with the rail portion. The body portions of the flanged bosses are separately movably received in the corresponding rail portions; the flange portions of the flanged bosses have a diameter larger than a diameter of the body portions and a width of the rail portions; and the diameter of the flange portions is smaller than a diameter of the quick-release hole portions.

According to the above embodiment, a distance between the two flanged bosses is larger than a distance between the two quick-release hole portions of the two quick-release guide rails.

According to another embodiment of the present invention, the first limiting unit is in the form of a guide rod and located at an end of the pulling member having the first pivot section formed thereat, the second limiting unit is in the form of a supporting seat provided with a guide rail, and the guide rod is engaged with the guide rail to move in along a path defined by the guide rail.

According to an embodiment of the present invention, the handle member includes a limiting section, which is located adjacent to the closing edge of the pressing section, and the first partitioning wall is correspondingly provided with a mating limiting section. The limiting section is adapted to limit the mating limiting section to stop the handle member from moving relative to the first partitioning wall.