In the third variation of the second embodiment, the handle member 120 includes a fixing section 125. When the handle member 120 is in the closed position, the fixing section 125 is used to temporarily fix the handle member 120 to the first partitioning wall 210. For example, the fixing section 125 can be a fastening bolt extended through the handle member 120. In this case, the first partitioning wall 210 is correspondingly provided with a fastening hole 215. To operate the handle member 120, first turn and loosen the fixing section 125 from the fastening hole 215 to allow the handle member 120 to be freely turned and moved.

In the third variation of the second embodiment, the first partitioning wall 210 has a stop flange 214 that is located corresponding to the operating section 123 of the handle member 120 when the latter is in the closed position. The stop flange 214 functions to stop the operating section 123 from moving into the first partitioning wall 210 and accordingly, hold the pulling member 110 in place. Preferably, the fixing section 125 is provided on the operating section 123 and the fastening hole 215 is provided on the stop flange 214 corresponding to the fixing section 125.

In the third variation of the second embodiment, the first partitioning wall 210 has a second limiting unit 212, which is in the form of an elongated hole. The pulling member 110 is extended through the second limiting unit 212 to move in along the second limiting unit 212. The second limiting unit 212 functions to limit a distance by which the pulling member 110 can be moved.