PURPOSE: To have bolt heat and strike resistance and expansibility in a staple and drive the staple against a weak wall so as to fix it thereat firmly by providing nail holes in both leg parts of a U-shape resinous covering material, and driving both legs of a U-shaped metal nail from opening ports of the both nail holes.

CONSTITUTION: A covering material A made of the resinous material having expansionability is formed in a U-shaped, and holes having a diameter a little smaller than legs 6, 6 of a metal nail B provided in a core of both legs 1, 1 of the covering material A, and the upper parts of both the legs 1, 1 are connected to each other with a connecting guard 3. A channel 4 covering the inside of a top part 8 of the metal nail B is formed in a top face of the connecting guard 3 to exposure the top part 8, and sharped ends 5 are formed in the tips of both the legs 1, 1 to facilitate a driving. The metal nail B has metal legs 6, 6 in the same shape of holes provided in the legs 1, 1 of the covering material A, and since these diameters are a little larger than the legs 1, 1 of the covering material A, the metal nail B resists the tensile force after being driven to stick to a weak wall 10 firmly.