Abstract: A screw having a primary thread extending along its shank and terminating at the screw head is formed with a supplemental thread extending between adjacent convolutions of the primary thread and also terminating at the head of the screw. The spaced termini of the two threads maintain a washer at the head in a position perpendicular to the axis of the shank of the screw.
Abstract: A fastener having a shank and head, the latter formed with a recess in its lower surface. A gasket is positioned in the recess, which it partially fills until the screw is employed to joint two elements and the gasket is compressed so that it fills the entirety of the recess, thereby preventing the ingress of undesirable materials.