The device is combination of a fastener and a splicing piece suited with the fastener. The fastener includes a post, a plurality of outer bosses, an outer slab, a first hole and a second inner flange. The plurality of outer bosses are provided in an upper portion of the post. The plurality of outer bosses include a first outer boss, a second outer boss and a third outer boss. The first outer boss is located under the second outer boss. At least a local portion of the splicing piece is a platy portion. Connecting through holes are provided in the platy portion. The connecting through holes include a first through hole. A first inner flange used for being clamped by a lower surface of the first outer boss and an upper surface of the second outer boss is provided on an inner wall of the first through hole.