Jan. 24th: Patent Description - Andrew McBride
Author: Andrew McBride
Patent number: 4697969
Filing date: Sep 6, 1985
Issue date: Oct 6, 1987
This patent claims an improved wood screw with either a flat head, hex head or phillips head, and having two flutes of semi-circular cross-section, the first beginning at the tip of the screw and ending near the head of the screw, and the second beginning at the tip of the screw and continuing a length of about three screw heads from the tip. Both flutes have a diameter about a third of the screw's root diameter, and the tangent lines to each flute axis form an angle of 30º with the screw's axis.