SCREW FOR USE IN CONCRETE

摘要

The concrete screw of the invention reduces the driving torque required, reduces shear failure, and provides increased pull-out resistance The screw has Hi-Low threads, the major thread being of greater diameter than the minor thread, the threads having a pitch displacement at least equal to the diameter of the screw shank Helical grooves of opposite rotational hand from the threads extend the length of the threaded portion of the screw, and have a pitch displacement at least two times the diameter of the screw shank In a limited portion adjacent the tip of the screw, and extending generally no more than 1/3 of the length of the threads, are intermediate helical counter-rotation grooves The intermediate grooves may be adjacent the principal grooves to produce a W-shaped notch in the threads Preferably, the W-shaped notch is asymmetrical in the direction of rotation of the grooves.