Annular dovetail head fastener

Claim 1

In combination, a fastener having a shank received in a work bore, and a head received in work counterbore, the shank extending in an axial direction rearwardly from the head, the improvement comprising (a) the head having an annular side wall received in said counterbore, (b) the head having a front end wall, and a rear wall that tapers radially outwardly and rearwardly, the rear wall spaced rearwardly from said front wall for engagement with a work surface that also tapers radially outwardly and rearwardly, (c) and including said work, the work having a first pre-formed counterbore facing the side wall of the head and extending parallel thereto, and a second counterbore which comprises said work surface that tapers radially outwardly and rearwardly and extends parallel to the head rear wall, the head rear wall engaging said work second counterbore surface, the work having an outer surface, and the perimeter of the head front wall being substantially flush with the work outer surface, (d) the head side wall tapering rearwardly and having tapered angularity between 0° and 15°, (e) the head rear wall having frusto-conical tapered angularity, relative to a plane normal to said axis, between 1° and 22°, and between loci closely proximate said shank and proximate said side wall, (f) the head rear wall merging convexly and annularly with the head side wall, the head thickness gradually and progressively diminishing radially inwardly from the locus of said convex merging to said locus proximate the shank which locus is annularly concave.