Abstract: A self-tapping screw for use on concrete and masonry structures is disclosed. The screw has a helically threaded shank of uniform diameter. The crest diameter of the helical thread on the shank has a taper which increases gradually from the tip or entering end of the shank for a predetermined distance along the shank and then has a uniform diameter over the remaining portion of the helical thread. The helical threads have a spacing of 5-8 threads per inch for screw sizes in the range of 1/2 to 3/16 inch. Thread cutting notches are formed in the threads over at least the tapered portion thereof. The screw is hardened to a Rockwell "C" hardness of 48 or greater.

Abstract: The disclosure relates to a method of insuring the tightness of a fastener including forming a three-dimensional annular member in an austenite phase using a press, cooling the annular member to a temperature lower than the temperature for starting an austenite transformation, fastening the fastener with the annular member to flatten the annular member, and returning the temperature of the annular member to a higher than austenite temperature so that the recovery power of the annular member for returning the annular member to the three-dimensional shape in the austenite phase generates a fastening force for the fastener.