Abstract A fastener comprising a screw having a head adapted to be engaged by means whereby it may be rotated so as to force it into a workpiece or the like at one end and a workpiece engaging point at the other end. This fastener is designed to have the maximum tensile strength in the total fastener. To this end the shank of the screw, between the point and head, is formed into three sections. The first section, moving from the point towards the head, is of relatively small diameter and is provided with a pair of cutting edges having flutes extending therefrom whereby this section functions as a pilot drill. The next or intermediate section is of larger diameter. The aforementioned grooves or flutes may extend into this section and define a second pair of cutting edges. This intermediate section is provided with its own cutting edges and flutes whereby this intermediate section constitutes a reaming section having multiple cutting edges with flutes extending therefrom. These drilling and reaming sections are designed to give a positive round hole of the proper diameter so that the threaded section can engage the sides of the hole and distort the sheet metal enough so that a firm fastening is accomplished. The third section, therefore, that immediately adjacent the head, is provided with self tapping screw threads of substantially constant diameter and uninterrupted by any grooves, flutes or the like.
In a fastener comprising a cylindrical shank having at one end a head to be engaged by a fastener driving tool and having at the other end a portion to engage a workpiece and the like; the improvement which comprises providing said shank with three separate sections extending from the workpiece engaging portion to the head, said sections comprising consecutively: a pilot drill of relatively small diameter and having a pair of cutting edges; a reamer of larger diameter and having additional cutting edges, said additional cutting edges being in the form of a plurality of knurls defined by the said flutes of said reamer, the last mentioned flutes being in the form of parallel grooves; and a constant diameter, uninterrupted self-tapping and holding threaded portion, the major diameter of the threads in said threaded portion being greater than the diameter of said reamer and the minor diameter of said threads being no greater than the diameter of said reamer; all of said cutting edges having flutes extending therefrom whereby to define said edges, all of said flutes terminating short of said threaded section.
Claim 2
Dependent Claim
184 words
In a fastener comprising a cylindrical shank having at one end a head to be engaged by a fastener driving tool and having at the other end a portion to engage a workpiece and the like; the improvement which comprises providing said shank with three separate sections extending from the workpiece engaging portion to the head, said sections comprising consecutively: a pilot drill of relatively small diameter and having a pair of cutting edges; a reamer of larger diameter and having additional cutting edges, said additional cutting edges being in the form of a plurality of knurls defined by the said flutes of said reamer, the last mentioned flutes being in the form of parallel grooves; and a constant diameter, uninterrupted self-tapping and holding threaded portion, the major diameter of the threads in said threaded portion being greater than the diameter of said reamer and the minor diameter of said threads being no greater than the diameter of said reamer; all of said cutting edges having flutes extending therefrom whereby to define said edges, all of said flutes terminating short of said threaded section.