| 摘要 |
A combination screw and clearance drill is provided that in one mode of operation is able to drill a pilot hole for the screw threads through a top piece of material and then screw into a lower piece of material, thus enabling the two pieces of material to be screwed tightly together in a single operation. The screw is designed in such a manner that the ability of the screw to drill a clearance hole for the threads does not substantially effect the gripping ability of the screw. In one direction of rotation the screw is able to drill the clearance hole for the threads of the screw and by reversing rotation the screw is able to stop drilling a clearance hole and function as a regular screw. Flutes in the screw head cut a counter bore for the head when the head contacts the surface of the top piece of material. |
