Abstract: An attachment for a percussive tool comprises a plurality of parallel rows of teeth (10) formed along the edges of planar chisel blades (9) arranged to form a shape having rotational symmetry. The attachment is connected to a percussive tool and placed in contact with a wall (12). The tool causes percussive action of the attachment such that the chisel blades (9) form a plurality of parallel grooves (13) and ridges in the wall. The tool and attachment are then rotated through an angle and placed in contact with the wall (12) in a position overlaying the plurality of parallel grooves (13). This breaks up the ridges forming a hole (15) of a substantially uniform depth. The attachment is used to produce square holes suitable for installing wall boxes for light switches or power points.