Roofing fastener and improved screw therefor

A composite fastener useful to fasten roofing materials to a substrate, the composite fastener comprising

• (a) a roofing screw having a head, a shank, and a tip and being made from a resilient material, the shank extending between the head and the tip and defining an axis, the shank having a leading portion joined to the tip and a locking portion joined to the leading portion, the locking portion having a transitional part and an additional part between the transitional part and the head, the leading portion being threaded so as to define a maximum crest diameter, the transitional part being substantially frusto-conical and defining a major diameter at the additional part and a minor diameter, the transitional part having at least one locking tab, which in a normal position extends axially toward the head and outwardly in a radial sense, beyond the maximum crest diameter and beyond the major diameter, in such manner that an imaginary cylinder being coaxial with the shank and having a diameter equal to the major diameter intersects the locking tab so as to divide the locking tab into a proximal part and a distal part, the locking tab being capable of flexing into a flexed position wherein the locking tab fits within an imaginary cylinder being coaxial with the shank and having a diameter equal approximately to the maximum crest diameter, and
• (b) a roofing washer having an aperture, which has a margin configured so as to define means coacting with the roofing screw, when the roofing screw is driven through the roofing washer, by allowing the leading portion to pass through the aperture, by flexing the locking tab from the normal position into the flexed position, such that the locking tab can pass through the aperture, when the roofing screw is driven sufficiently for the locking portion to extend through the aperture, and by allowing the locking tab to flex back toward the normal position when the roofing screw is driven sufficiently for the head to be nearly contiguous with or to bear against the roofing washer,
• whereby the substantially frusto-conical, transitional part tends to center the roofing screw relative to the aperture of the roofing washer so as to protect the locking tab against being broken accidentally by being driven against the roofing washer at the margin of the aperture, and whereby the roofing screw becomes locked to the roofing washer, by the locking tab, when the roofing screw is driven sufficiently for the head to be nearly contiguous with or to bear against the roofing washer.