Abstract: A box includes a base and a cover which is removably mounted to the base. The base includes a first room defined therein, and a connection strip extends from the periphery of the top opening of the base. A knob is formed on the connection strip. The cover includes a skirt extending from the periphery thereof so as to form a second room between the skirt and the cover. The skirt includes a U-shaped recess formed in the outside thereof such that the knob can be engaged with the U-shaped recess. The U-shaped recess includes a U-shaped inside wall formed between two outwardly projecting reinforcement ribs on the outside of the skirt to easily accommodate the knob therebetween.