Blind fastener with work gripping head

Claim 1

In a tubular fastener having an axially extending tubular shank receivable in a work bore and an annular head receivable in forcible engagement with the work material forming a counterbore, and in combination with said work, the improvement comprising (a) the head having an annular end face, a first forwardly tapered section located forwardly of said end face to forcibly engage the work counterbore and a second forwardly tapered section located forwardly of the first section, the taper angularity of the second section substantially exceeding the taper angularity of the first section, (b) a stem extending through the tubular shank and head and (c) means responsive to retraction of the stem toward the head end of the fastener to expand at the opposite end of the fastener and axially retain the fastener in position with the head first section forcibly engaging the counterbore, (d) said forcible engagement of the head first forwardly tapered section with the work counterbore acting to create radial compression exerted on the stem to prevent loosening of the stem relative to the head and shank, (e) the head first section having sufficient forcible engagement with the counterbore as to develop friction acting to block rotation of the head in response to torque application to the stem during said stem retraction, there being interference between said first section and counterbore between 0.001 and 0.010 inches, (f) the taper angularity of the first section being greater than 2° and less than 15°, and the axial length of the first section being within the range 0.140 inches to 0.010 inches, said selected length increasing within said length range as said selected angularity decreases within said angle range, the entirety of said axial length being radially outwardly spaced of and from a taper formed by the head and spaced outwardly of the stem.