Threaded fastener with torque control head

Claim 2

A fastener comprising: a screw threaded shank; two driving heads integral with said shank and including a first head for seating said fastener, and a second head for unseating said fastener, each driving head including a plurality of radial variations which define tool engaging surfaces, the radial variations on said first driving head defining the tool engaging surfaces being provided by an internal socket which defines a circumferential wall, with the radial variations on said second driving head being on the exterior thereof, wherein said tool engaging surfaces provided by the radial variations include a plurality of inwardly extending projections defined by a first series of arcuately curved surfaces alternating with a second series of arcuately curved surfaces curving in an opposite direction, the two said series being disposed symmetrically about the central axis of said fastener, the cross-sectional area through the tool engaging surfaces of said second driving head being greater than that of said shank, such that said second driving head has a torsional breaking strength greater than that of said shank, and said first driving head having a crosssectional area through its tool engaging surfaces that is less than the cross-sectional area of said shank, said first driving head correspondingly having a torsional breaking strength less than said shank, said first head being disposed axially outwardly of said second head and joined directly thereto in the absence of an intervening neck portion having a lesser cross-sectional area than said first driving head, such that upon seating of said fastener, said first driving head will fail in shear across said tool engaging surfaces before said shank or said second driving head, the torsional breaking strength of said first driving head being determined so that said head will fail in shear when the driving torque applied thereto, approximates a pre-selected value, which is sufficient under predetermined driving conditions to drive said fastener into a parent body and place said shank under a predetermined tensile load without stripping the threads on said shank.

Claim 3

A fastener as defined in claim 1 wherein said internal socket extends axially inward to a depth sufficient to permit a tool to be engaged therein, but insufficient to permit engagement of said tool with said second driving head such that the seating torque applied by said tool is applied to said first driving head whereby the circumferential wall structure of said first driving head will fail in shear prior to failure of said shank or said second driving head.

Claim 4

A fastener as defined in claim 1, wherein said projections are six in number to provide a hex-lobular array.

Claim 5

A fastener comprising: a screw threaded shank; two driving heads integral with said shank and including a first head for seating said fastener, and a second head for unseating said fastener, each driving head including a plurality of radial variations which define tool engaging surfaces; said tool engaging surfaces on said first head including a plurality of outwardly disposed projections defined by a first series of arcuately curved surfaces alternating with a second series of arcuately curved surfaces curving in a direction opposite that of the first series, the two said series being disposed symmetrically in a lobular array about the central axis of said fastener, the cross-sectional area through the tool engaging surfaces of said second driving head being greater than that of said shank, such that said second driviNg head has a torsional breaking strength greater than that of said shank, and said first driving head having a cross-sectional area through its tool engaging surfaces that is less than the cross-sectional area of said shank, said first driving head correspondingly having a torsional breaking strength less than said shank, said first head being disposed axially outwardly of said second head and joined directly thereto in the absence of an intervening neck portion having a lesser cross-sectional area than said first driving head, such that upon seating of said fastener, said first driving head will fail in shear across said tool engaging surfaces before said shank or said second driving head, the torsional breaking strength of said first driving head being determined so that said head will fail in shear when the driving torque applied thereto, approximates a preselected value, which is sufficient under predetermined driving conditions to drive said fastener into a parent body and place said shank under a predetermined tensile load without stripping the threads on said shank.

Claim 6

A fastener comprising: a screw threaded shank; two driving heads integral with said shank and including a first head for seating said fastener, and a second head for unseating said fastener, each driving head including a plurality of radial variations which define tool engaging surfaces; said tool engaging surfaces on said first head including a plurality of outwardly disposed projections defined by a first series of arcuately curved surfaces alternating with a second series of arcuately curved surfaces curving in a direction opposite that of the first series, the two said series being disposed symmetrically in a lobular array about the central axis of said fastener, the cross-sectional area through the tool engaging surfaces of said second driving head being greater than that of said shank, such that said second driviNg head has a torsional breaking strength greater than that of said shank, and said first driving head having a cross-sectional area through its tool engaging surfaces that is less than the cross-sectional area of said shank, said first driving head correspondingly having a torsional breaking strength less than said shank, said first head being disposed axially outwardly of said second head and joined directly thereto in the absence of an intervening neck portion having a lesser cross-sectional area than said first driving head, such that upon seating of said fastener, said first driving head will fail in shear across said tool engaging surfaces before said shank or said second driving head, the torsional breaking strength of said first driving head being determined so that said head will fail in shear when the driving torque applied thereto, approximates a preselected value, which is sufficient under predetermined driving conditions to drive said fastener into a parent body and place said shank under a predetermined tensile load without stripping the threads on said shank.

Claim 7

A fastener as defined in claim 4 further including an intermediate portion disposed axially inward of said tool engaging surfaces and joining said first driving head directly to said second driving head, said intermediate portion having a cross-sectional area greater than that of said tool engaging portion and correspondingly a torsional breaking strength greater than that of said tool engaging portion.

Claim 8

A fastener as defined in claim 4 wherein said projections are six in number providing a hex-lobular array.

Claim 9

A fastener comprising: a screw threaded shank a pair of tandem, integral driving heads with a first driving head for initially seating said fastener and a second driving head for unseating said fastener, each said driving head having a plurality of tool engaging surfaces formed thereon, with the surfaces on said first driving head being defined by a plurality of radial projections, and being disposed generally parallel to the axis of the fastener, said tool engaging surfaces on said first head including six projections defined by a first series of arcuately curved surfaces alternating with a second series of arcuately curved surfaces curving in a direction opposite that of the first series, the two said series being disposed symmetrically in a hex-lobular array about the central axis of said fastener, said second driving head having a cross-sectional area through said tool engaging surfaces thereof which is greater than that of said shank, said second driving head therefore having a torsional breaking strength greater than that of said shank, and said first driving head having a cross-sectional area through the tool engaging surfaces thereof that is less than that of said shank, thereby providing said first driving head with a torsional breaking strength less than that of said shank and said second head, said first driving head being disposed axially outward of said second head and joined directly thereto in the absence of an intervening neck portion of lesser cross-sectional area than any portion of said first driving head, said first driving head including a tool engaging portion having said tool engaging surfaces formed thereon and an intermediate portion joining said first driving head directly to said second driving head, said intermediate portion having a cross-sectional area greater than that of said tool engaging portion and correspondingly greater torsional breaking strength than said tool engaging portion whereby upon seating of said fastener, said first head will fail in shear across the tool engaging surfaces thereof proximate the juncture of said tool engaging portion and said intermediate portion before failure of said shank or said second driving head.

Claim 10

A fastener comprising: a screw threaded shank a pair of tandem, integral driving heads with a first driving head for initially seating said fastener and a second driving head for unseating said fastener, each said driving head having a plurality of tool engaging surfaces formed thereon, with the surfaces on said first driving head being defined by a plurality of radial projections, and being disposed generally parallel to the axis of the fastener, said tool engaging surfaces on said first head including six projections defined by a first series of arcuately curved surfaces alternating with a second series of arcuately curved surfaces curving in a direction opposite that of the first series, the two said series being disposed symmetrically in a hex-lobular array about the central axis of said fastener, said second driving head having a cross-sectional area through said tool engaging surfaces thereof which is greater than that of said shank, said second driving head therefore having a torsional breaking strength greater than that of said shank, and said first driving head having a cross-sectional area through the tool engaging surfaces thereof that is less than that of said shank, thereby providing said first driving head with a torsional breaking strength less than that of said shank and said second head, said first driving head being disposed axially outward of said second head and joined directly thereto in the absence of an intervening neck portion of lesser cross-sectional area than any portion of said first driving head, said first driving head including a tool engaging portion having said tool engaging surfaces formed thereon and an intermediate portion joining said first driving head directly to said second driving head, said intermediate portion having a cross-sectional area greater than that of said tool engaging portion and correspondingly greater torsional breaking strength than said tool engaging portion whereby upon seating of said fastener, said first head will fail in shear across the tool engaging surfaces thereof proximate the juncture of said tool engaging portion and said intermediate portion before failure of said shank or said second driving head.