Abstract A screw fastener formed with improved thread construction adapted to provide a staged or graduated entry into a workpiece. The fastener comprises a shank section formed with an integral driving head at one end and a tapered or conical point section at the other end, and a raised helical thread extending from near the tip of the conical point substantially throughout the length of the point and shank sections. The diameter of the thread increases gradually from the point tip along the length of the conical surface and then decreases in diameter - or increases at a lesser degree - as it approaches the cylindrical shank section. The fastener may also comprise a second raised helical thread, parallel to and lying within the first thread and extending from near the junction of the conical point section and the cylindrical shank section substantially throughout the length of the shank. The leading edge of the second thread extends part-way down the conical point and overlaps axially the decreasing diameter portion of the first thread. A modified version of the present invention includes a screw of the type described with a relatively short lead screw formed on the point near the tip and a substantial gap with no threads along the conical point surface leading to the shank section. This modification is intended primarily for joining lamina together.
A screw fastener element having an integral elongate shank portion formed with a driving head at one end and a conical point portion at the other end and adapted to provide a stage penetration into a work-piece, the improved thread construction comprising: a first raised helical thread formed on the exterior of the conical point and shank portions and having a generally uniform thread height throughout the length of said shank portion, and having a leading edge extending from near the tip of the conical point and a gradually increasing thread height throughout a portion of the axial length of the conical point; and said thread height on said conical point decreasing in elevation relative to the increasing diameter of the conical point and diminishing substantially to zero elevation adjacent the juncture of said shank and conical point portions.
Claim 2
Dependent Claim
139 words
A screw fastener element having an integral elongate shank portion formed with a driving head at one end and a conical point portion at the other end and adapted to provide a stage penetration into a work-piece, the improved thread construction comprising: a first raised helical thread formed on the exterior of the conical point and shank portions and having a generally uniform thread height throughout the length of said shank portion, and having a leading edge extending from near the tip of the conical point and a gradually increasing thread height throughout a portion of the axial length of the conical point; and said thread height on said conical point decreasing in elevation relative to the increasing diameter of the conical point and diminishing substantially to zero elevation adjacent the juncture of said shank and conical point portions.
Claim 3
Dependent Claim
67 words
The screw fastener element of claim 1 including: a second raised helical thread formed on the exterior of the shank portion and lying within and parallel to said first thread and having a thread height substantially equal to the thread height of said first thread on said shank portion, and also having a leading edge extending from near the juncture of said shank and conical point portions.
Claim 4
Dependent Claim
33 words
The screw fastener element of claim 2 wherein: said leading edge of said second helical thread commences on said conical point portion and overlaps axially the decreasing elevation portion of said first thread.