| 摘要 |
According to the invention, at least two cutting blades (3a, 3b) are attached to a body (4) on the opposite sides of a centre bit (2) at substantially an equal distance from the centre bit (2). The cutting point (6a) of the first blade (3a) is on the outer edge of the blade (3a), and the cutting point (6b) of the second cutting blade (3b) is on the inner edge of the cutting blade (3b) whereby, when a hole is drilled, a wide cut is formed in the object drilled by the action of the cutting blades (3a, 3b). |
