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It is special because there is a little protruding round shape on one side of the silica gel case and the number of protruding rounds on each silica gel holder is particular. So, when incapable of differentiating a proper key to open a door due to a variety of reasons, we can easily recognize the right key by the raising round shape of different silica gel holders put around keys. Besides, the semicircle on which the raising area is has the quality of directing, consequently, we can once only thrust a key into a key hole exactly and then open the door successfully after touching the according key hole.