Patent Description:
Patent document <CIT> describes a drilling and thread cutting screw having a drill point including generally concave surfaces forming flutes therein with discrete obstructions formed on the concave surfaces to effectively break chips produced by cutting edges in the drill point.

There is a continuing need for self-drilling self-tapping fasteners that have improvements to performance in one or more of the following categories without decreasing performance in any of the other categories: (i) drilling times; (ii) ductility; (iii) tapping torque; (iv) torsional strength; (v) tensile strength; and (vi) pullout force.

The present disclosure provides a self-drilling self-tapping fastener that has: (<NUM>) an improved performance in drilling time and specifically a relatively lower drilling time, and (<NUM>) improved performance in pullout force and specifically a relatively higher pullout force, both without decreasing performance in any of the ductility, the tapping torque, the torsional strength, and the tension strength of such self-drilling self-tapping fastener.

In various embodiments of the present disclosure, the self-drilling self-tapping fastener includes a head, a shank integrally connected to and extending from the head and including a first shank portion and a second shank portion, and a helical thread formation integrally connected to and extending radially outwardly from the first shank portion and part of the second shank portion. The second shank portion defines a longitudinally extending first flute and a longitudinally extending second flute. The first flute extends through three threads of the thread formation on a first side of the second shank portion The second flute extends through three threads of the thread formation on a second side of the second shank portion and to a fourth thread formation on the second side of the second shank portion. The second shank portion includes a first chip breaker positioned in the first flute and a second chip breaker positioned in the second flute. The second shank portion includes a drill tip. The drill tip includes a first cutting blade having a first cutting edge and a second cutting blade having a second cutting edge. The first cutting edge and the second cutting edge are tapered toward each other. The second shank portion is suitably formed such as by milling or forging in various different embodiments of the present disclosure. The head, the shank, and the helical thread formation are specifically configured and sized such that the self-drilling self-tapping fastener has improved performance in drilling time and pullout force without decreased performance in any of the ductility, the tapping torque, the torsional strength, and the tension strength of the self-drilling self-tapping fastener.

Other objects, features, and advantages of the present disclosure will be apparent from the following detailed disclosure and accompanying drawings.

While the systems, devices, and methods described herein may be embodied in various forms, the drawings show and the specification describes certain exemplary and non-limiting embodiments. Not all components shown in the drawings and described in the specification may be required, and certain implementations may include additional, different, or fewer components. Variations in the arrangement and type of the components; the shapes, sizes, and materials of the components; and the manners of connections of the components may be made without departing from the scope of the claims Unless otherwise indicated, any directions referred to in the specification reflect the orientations of the components shown in the corresponding drawings and do not limit the scope of the present disclosure. Further, terms that refer to mounting methods, such as mounted, connected, etc., are not intended to be limited to direct mounting methods but should be interpreted broadly to include indirect and operably mounted, connected, and like mounting methods. This specification is intended to be taken as a whole and interpreted in accordance with the principles of the present disclosure and as understood by one of ordinary skill in the art.

Turning now to the drawings, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> illustrate one example embodiment of the self-drilling self-tapping fastener of the present disclosure, generally indicated by numeral <NUM> and sometimes called the "fastener" herein for brevity. <FIG> and <FIG> show tables comparing the features and dimensions of the self-drilling self-tapping fastener <NUM> to six example commercially available self-drilling fasteners. <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> show tables comparing various tests results on the self-drilling self-tapping fastener <NUM> to these same six example commercially available self-drilling self-tapping fasteners.

Various embodiments of the example fastener <NUM> are particularly configured for use in connecting steel objects (such as but not limited to connecting a <NUM>/<NUM> inch (<NUM> cms) steel plate to a <NUM>/<NUM> inch (<NUM> cms) steel plate). However, the fastener may be employed for a variety of different uses in accordance with the present disclosure. In this example, fastener <NUM> is a #<NUM>-<NUM> x <NUM>-<NUM>/<NUM> inch fastener. It should be appreciated that the fastener length may vary in other alternative embodiments of the present disclosure as further discussed below.

The fastener <NUM> has a longitudinal central axis X and includes: (a) a head <NUM>; (b) a shank <NUM> integrally connected at one end to the head <NUM>; and (c) a helical thread formation <NUM> integrally connected to and extending outwardly from parts of the shank <NUM>. The shank <NUM> includes a first shank portion <NUM> integrally connected to and extending from the head <NUM>, and a second shank portion <NUM> integrally connected to and extending from the first shank portion <NUM> opposite the head <NUM>. Line C in <FIG> illustrates the plane along which the first shank portion <NUM> is integrally connected to the second shank portion <NUM> in this example embodiment. The second shank portion <NUM> functions as the drilling portion of the shank <NUM> and enables the fastener <NUM> to be used to drill a hole in one or more objects into which the fastener <NUM> will be tapped, fastened and secured.

In this example embodiment, the head <NUM>, the shank <NUM>, and the thread formation <NUM> are monolithically formed. More specifically, in this example embodiment, the fastener <NUM> is made by: (<NUM>) cutting (or otherwise forming) a carbon steel member (not shown but further described below) that is sometimes initially called a blank having a suitable length and a suitable width; (<NUM>) then forming (such as by forging) the carbon steel member to form the head <NUM>; (<NUM>) then forming (such as by forging or milling) the carbon steel member to form the second shank portion <NUM>; (<NUM>) then forming (such as by roll threading) the carbon steel member to form the thread formation <NUM>; (<NUM>) then heat treating the carbon steel member; and (<NUM>) then coating the carbon steel member with a suitable corrosion resistance coating and curing this coating on the carbon steel member. It should be appreciated that one or more suitable cleaning and/or deburring processes may be employed in accordance with the present disclosure to form the fastener <NUM>.

It should be appreciated that the self-drilling self-tapping fastener <NUM> of this example embodiment is made from a low carbon steel (such as but not limited to an AISI <NUM> low carbon steel). It should be also be appreciated that the heat treatment of case hardening is to provide a hardened fastener surface, so that the fastener point can self-drill into steel objects, and the thread formation can self-tap its own way to engage with steel objects. It should further be appreciated that hardened fastener surface case depth should be maintained in a reasonable range because if the case depth is too deep, it can make the fastener too brittle. It should also be appreciated that the case hardening process also provides a lower fastener core hardness, which ensures that the fastener has enough ductility. If the core hardness is too high, it will make the fastener too brittle, and become vulnerable to hydrogen embrittlement failure and/or hydrogen assisted stress corrosion. It should further be appreciated that the fastener's coating not only provides corrosion protection, but also provides lubrication when the fastener drills into one or more steel objects.

The head <NUM> includes a generally annular bottom portion <NUM> and a top portion <NUM> integrally connected to the bottom portion <NUM>. The annular bottom portion <NUM> has an outer diameter of <NUM> inches (<NUM> cms) and a height of <NUM> inches (<NUM> cms). The annular bottom portion <NUM> has a bottom surface <NUM>, a top surface <NUM>, and a generally cylindrical outer edge <NUM> extending from and connect the bottom surface <NUM> to the top surface <NUM>. The outer edge <NUM> is somewhat rounded or convex along its entire surface. The bottom portion <NUM> is also integrally connected to the first shank portion <NUM>. In this example embodiment, as best shown in <FIG>, the top portion <NUM> of the head <NUM> defines an external hexagonal mechanical engaging structure having six sides 142a, 142b, 142c, 142d, 142e, and 142f that define an upper recessed portion <NUM>. The six sides 142a, 142b, 142c, 142d, 142e, and 142f are engageable by an appropriate wrench or hex socket (not shown) configured to rotate and drive the self-drilling self-tapping fastener <NUM>. It should be appreciated that other suitable mechanical engaging structures (not shown) may be employed in accordance with the present disclosure, such as but not limited to: (<NUM>) a straight slot (engageable by a flathead screwdriver), (<NUM>) a cross-shaped slot (engageable by a Phillips head screwdriver), (<NUM>) an internal star or six lobe shaped cavity (engageable by a six lobe driver), or (<NUM>) an internal hexagonal shaped cavity (engageable by an Allen wrench). As also best shown in <FIG>, the top portion <NUM> of the head <NUM> has six corners 144a, 144b, 144c, 144d, 144e, and 144f, respectively between sides 142a and 142b, 142b and 142c, 142c and 142d, 142d and 142e, 142e and 142f, and 142f and 142a.

In this example embodiment, the top portion <NUM> of the head <NUM> has a height of <NUM> inches (<NUM> cms). The top portion <NUM> has an outer diameter of <NUM> inches (<NUM> cms) from side 142a to side 142d, from side 142b to side 142e, and from side 142c to side 142f. The top portion <NUM> has an outer diameter of <NUM> inches (<NUM> cms) from corner 144a to corner 144d, from corner 144b to corner 144e, and from corner 144c to corner 144f.

The shank <NUM> has a length (LS) indicated in <FIG>, which in this example embodiment is <NUM> inches (<NUM> cms), and includes: (<NUM>) the first shank portion <NUM>; and (<NUM>) the second shank portion <NUM>.

The first shank portion <NUM> is integrally connected to the head <NUM> at an inner end <NUM> and is integrally connected to the second shank portion <NUM> at an outer end <NUM>. The first shank portion <NUM> is annular and has a constant outer diameter (OD) from the inner end <NUM> (adjacent to the head <NUM>) to the outer end <NUM> (adjacent to the second shank portion <NUM>). This outer diameter in this example embodiment is <NUM> inches (<NUM> cms). The first shank portion <NUM> has a length (LFSP) as indicated in <FIG> and which in this example embodiment is <NUM> inches (<NUM> cms).

The second shank portion <NUM> includes an inner end <NUM> that is integrally connected to the first shank portion <NUM> and an outer end <NUM>. The outer end <NUM> is a free end and includes a drill tip <NUM> as described below. The second shank portion <NUM> is configured to enable the fastener <NUM> to be self-drilling. In particular, the second shank portion <NUM>: (<NUM>) defines a longitudinally extending first flute <NUM> (best seen in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>); (<NUM>) defines a longitudinally extending second flute <NUM> (best seen in <FIG>, <FIG>, <FIG>, and <FIG>); (<NUM>) includes a first chip breaker <NUM> (best seen in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>); (<NUM>) includes a second chip breaker <NUM> (best seen in <FIG>, <FIG>, <FIG>, and <FIG>); and (<NUM>) includes the drill tip <NUM>.

The second shank portion <NUM> is partially annular and has multiple different outer surfaces and outer diameters, as further described below. In this example embodiment, the second shank portion <NUM> has a length (LSSP) indicated in <FIG>, and which in this example embodiment is <NUM> inches (<NUM> cms). When viewed from the side shown in <FIG>, <FIG>, <FIG>, and <FIG>, and the side shown in <FIG>, <FIG>, and <FIG>, the second shank portion <NUM> has a first constant outer diameter until reaching the drill tip <NUM>. When viewed from the side shown in <FIG> and <FIG>, and the side shown in <FIG>, the second shank portion <NUM> has a first decreasing outer width, until reaching the drill tip <NUM>. This decreasing outer width first decreases as at a greater angle and then decreases at a smaller angle. The elongated opposite outer surfaces <NUM> and <NUM> of the second shank portion <NUM> are rounded or convex and extend between the respective opposite flutes <NUM> and <NUM>.

The first flute <NUM> defined in the second shank portion <NUM> includes a longitudinally extending first surface <NUM> and a longitudinally extending second surface <NUM>. The longitudinally extending first surface <NUM> and the longitudinally extending second surface <NUM> meet along a longitudinally extending connection line <NUM> (best seen in <FIG>, <FIG>, <FIG>, and <FIG>). The first flute <NUM> narrows almost to a point at the first end <NUM> of the second shank portion <NUM>, widens toward the central section (not labeled) of the second shank portion <NUM>, and remains wide through the drill tip <NUM> to the second end <NUM> of the second shank portion <NUM> (as best seen in <FIG>, <FIG>, <FIG>, and <FIG>).

Likewise, the second flute <NUM> defined in the second shank portion <NUM> includes a longitudinally extending first surface <NUM> and a longitudinally extending second surface <NUM>. The longitudinally extending first surface <NUM> and the longitudinally extending second surface <NUM> meet along a longitudinally extending connection line <NUM> (best seen in <FIG>, <FIG>, <FIG>, and <FIG>). The second flute <NUM> narrows almost to a point at the first end <NUM> of the second shank portion <NUM>, widens toward the central section (not labeled) of the second shank portion <NUM>, and remains wide through the drill tip <NUM> to the second end <NUM> of the second shank portion <NUM> (as best seen in <FIG>, <FIG>, and <FIG>).

The first and second flutes <NUM> and <NUM> provide part of the self-drilling functionality of the fastener <NUM>, and particularly provide areas for the debris cut by the drill tip <NUM> and the chip breakers <NUM> and <NUM> to move along the length of the shank <NUM> of the fastener <NUM> and out of the hole(s) being formed by the fastener <NUM> in the objects to which the fastener will be tapped, fastened, and secured.

For each flute <NUM> and <NUM>, the flute length in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P1 indications on <FIG> and <FIG> and on Table <NUM> (<FIG>). It should be appreciated that this length is <NUM> inches (<NUM> cms) longer than the flute length of example Fastener-A as shown in <FIG>. This longer flute length in part enables the fastener <NUM> to be drilled through one or more thicker objects.

For each flute <NUM> and <NUM>, the flute angle in this example embodiment is <NUM> degrees at one or more designated points along each respective flute. This is indicated by the P2 indications on <FIG> and <FIG> and on Table <NUM> (<FIG>).

For each flute <NUM> and <NUM>, the flute relief length in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P3 indication on <FIG> and on Table <NUM> (<FIG>).

As best shown in <FIG>, the first chip breaker <NUM> of the second shank portion <NUM> includes first, second, third, and fourth connected surfaces <NUM>, <NUM>, <NUM>, and <NUM> positioned in the flute <NUM> adjacent the second end <NUM> of the second shank portion <NUM>. Likewise, as best shown in <FIG>, the second chip breaker <NUM> of the second shank portion <NUM> includes first, second, third, and fourth connected surfaces <NUM>, <NUM>, <NUM>, and <NUM> positioned in the flute <NUM> adjacent the second end <NUM> of the second shank portion <NUM>. These chip breakers <NUM> and <NUM> of the second shank portion <NUM> reduce tapping torque by cutting chips into smaller pieces from the object(s) that the fastener <NUM> is/are tapping into, which in turn reduces jamming. The chip breakers <NUM> and <NUM> thus provide part of the self-drilling functionality of the fastener <NUM>, and particularly function with the drill tip <NUM> to form the hole(s) in the object(s) being formed by the fastener <NUM> in the object(s) to which the fastener will be tapped, fastened, and secured.

The drill tip <NUM> of the second shank portion <NUM> extends from a transition plane indicated by dotted reference line TP shown in <FIG>, <FIG>, and <FIG> to the drill tip point <NUM>. The drill tip <NUM> has a length (LDT) or point height P7 indicated in <FIG> and <FIG> and on Table <NUM> (<FIG>) which in this example embodiment is <NUM> inches (<NUM> cms).

As best shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, the drill tip <NUM> includes: (<NUM>) a first cutting blade <NUM> having a first cutting edge <NUM>, a first cutting surface <NUM>, and an outer surface <NUM>; and (<NUM>) a second cutting blade <NUM> having a second cutting edge <NUM>, a first cutting surface <NUM>, and an outer surface <NUM>. The first cutting blade <NUM> and the second cutting blade <NUM> are tapered toward each other and specifically the first cutting edge <NUM> and the second cutting edge <NUM> are tapered toward each other.

The outer diameter of the drill tip <NUM> decreases moving along the longitudinal axis X in the direction of or toward the pointed end <NUM> from: (<NUM>) a point outer diameter (OD) adjacent the transition plane TP of <NUM> inches (<NUM> cms) indicated by the P5 indication on <FIG> and <FIG>, to (<NUM>) an outer diameter of <NUM> inches (<NUM> cms) at the drill point <NUM> indicated by the P11 indication on <FIG>.

As best shown in <FIG> and <FIG>, the first cutting edge <NUM> extends at an angle P8 to the outer surface of the second shank portion <NUM>. The second cutting edge <NUM> also extend at an angle P8 to the outer surface of the second shank portion <NUM>. In this example embodiment, P8 which is called the point cutting edge angle is <NUM> degrees.

It should be appreciated that in this example embodiment, the drill tip <NUM> has a rounded point (and particularly a slightly rounded point). In certain embodiments, the drill tip <NUM> point is formed as a sharp point and slightly rounded during a finishing manufacturing process. In other embodiments, the drill tip <NUM> is otherwise suitably rounded or formed. In other embodiments of the present disclosure, the drill tip <NUM> is not rounded but rather formed with a sharp point.

It should also be appreciated that in this example embodiment, the drill tip <NUM> is preferably directly positioned along the longitudinal axis X as shown in <FIG>, <FIG>, <FIG>, and <FIG>, but may slightly vary from being along the longitudinal axis due to manufacturing tolerances.

The relief angle of the drill tip <NUM> in this example embodiment is <NUM> degrees. This is indicated by the P4 indication on <FIG> and <FIG> and on Table <NUM> (<FIG>).

The point thickness of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P6 indication on <FIG> and on Table <NUM> (<FIG>).

The point flute angle of the drill tip <NUM> in this example embodiment is <NUM> degrees. This is indicated by the P9 indication on <FIG> and on Table <NUM> (<FIG>).

The drill point's web thickness of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is referred to herein as the drill point web thickness. This is indicated by the P10 indication on <FIG> and on Table <NUM> (<FIG>).

The center distance of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P11 indication on <FIG> and on Table <NUM> (<FIG>).

The flute detail radius of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P12 indication on <FIG> and on Table <NUM> (<FIG>).

The point outside radius of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the P13 indication on <FIG> and on Table <NUM> (<FIG>).

The point eccentricity or total indicator reading (TIR) of the drill tip <NUM> in this example embodiment is <NUM> inches (<NUM> cms) (but can be up to <NUM> inches (<NUM> cms) due to manufacturing tolerances) in accordance with the present disclosure. This is indicated by the P14 indication on Table <NUM> (<FIG>). It should be appreciated that for the purposes of the present disclosure, the point eccentricity or TIR is the difference between the maximum and minimum measurement readings of an indicator on the planar or cylindrical contoured surfaces of the drill tip <NUM> representing its/their respective amount(s) of deviation from flatness or roundness. It should also be appreciated that the extremely low point eccentricity or TIR of the drill tip <NUM> of the present disclosure maximizes the rotation of the second shank portion <NUM> with minimal deviation from along the longitudinal center axis X of the first and second shank portions <NUM> and <NUM> of fastener <NUM>. In various embodiments, this extremely low point eccentricity or TIR of the drill tip <NUM> is at least partially achieved in the fastener <NUM> by forging the second shank portion <NUM> of the fastener <NUM>, but it should be appreciated that such extremely low point eccentricity or TIR of the drill tip <NUM> could alternatively be achieved in the fastener <NUM> by milling the second shank portion <NUM> of the fastener <NUM> with extremely tight manufacturing tolerances. This configuration of the drill tip <NUM> and the second shank portion <NUM> is at least partially responsible for the relatively lower drilling time provided by the fastener <NUM> of the present disclosure. This configuration provides a more precise tapped thread (and/or slightly smaller hole(s)) in the object(s) in which the fastener <NUM> is tapped, fastened, and secured. This more precise tapped thread in the object(s) in combination with the enhanced thread engagement provided by the thread formation <NUM> (as described below) of the fastener <NUM> is considered to be at least partially responsible for the relatively higher pullout force provided by the fastener <NUM> of the present disclosure.

The helical thread formation <NUM> is integrally connected to and extends radially outwardly from respective sections of both the first and second portions <NUM> and <NUM> of the shank <NUM>. In this illustrated embodiment, the helical thread formation <NUM> extends along substantially the entire first shank portion <NUM> and an initial part of the second shank portion <NUM>. The helical thread formation <NUM> includes: (<NUM>) a first helical thread portion <NUM>; and (<NUM>) a second helical thread portion <NUM>.

The helical thread formation <NUM> has a substantially constant outer diameter from start of the thread formation <NUM> adjacent to the head <NUM> to almost the end of the thread formation <NUM> on the second shank portion <NUM>. At the third thread from the end of the thread formation <NUM> on the second shank portion <NUM>, the outer diameter or height of the thread formation <NUM> begins to decrease until gradually terminating at the outer surface of the second shank portion <NUM>. In other words, once reaching that point, the outer diameter of the thread formation <NUM> tapers radially inwardly until reaching the outer surface of the second shank portion <NUM>.

The helical thread formation <NUM> has a length (LHTF) indicated on <FIG> which in this example embodiment is <NUM> inches (<NUM> cms). This is also indicated by the T4 indication on <FIG> and in <FIG> Table <NUM>.

The root diameter to the head of the helical thread formation <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the T2 indication on <FIG> and on Table <NUM> (<FIG>).

The thread outer diameter (OD) of the helical thread formation <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the T3 indication on <FIG> and <FIG> and on Table <NUM> (<FIG>).

The pitch distance of the helical thread formation <NUM> in this example embodiment is <NUM>-<NUM> tpi (and preferably <NUM> threads per inch (<NUM> threads per cm). This is indicated by the T5 indication on <FIG> and on Table <NUM> (<FIG>).

The root outer diameter (OD) of the helical thread formation <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the T6 indication on <FIG> and <FIG> and on Table <NUM> (<FIG>).

The blank outer diameter (OD) of the helical thread formation <NUM> in this example embodiment is <NUM> inches (<NUM> cms). This is indicated by the T7 indication on Table <NUM> (<FIG>).

The thread at run-out of the helical thread formation <NUM> in this example embodiment is <NUM> thread, which means the thread outer diameter gradually decreased and merges with shank. This is indicated by the T8 indication on <FIG> and <FIG> and on Table <NUM> (<FIG>).

The quantity of threads of the helical thread formation <NUM> that are adjacent the flutes in this example embodiment is <NUM> threads. This is indicated by the T9 indication on <FIG> and <FIG> and on Table <NUM> (<FIG>).

The thread up taper of the helical thread formation <NUM> in this example embodiment is <NUM> (<NUM> cms). This is indicated by the T10 indication on Table <NUM> (<FIG>).

As mentioned above, the fastener <NUM> of the present disclosure provide a plurality of advantages. These advantages are shown in the tables discussed below. These tables are based on actual comparison tests on six commercially available self-drilling self-tapping fasteners and the fastener <NUM>. More specifically, as shown in Tables <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> respectively provided in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, the fastener <NUM> has: (<NUM>) an improved performance in drilling time and specifically a relatively lower drilling time, and (<NUM>) an improved performance in pullout force and specifically a relatively higher pullout force, both without decreasing performance in any of the ductility, the tapping torque, the torsional strength, and the tension strength of the fastener <NUM>, in comparison to such other fasteners.

More specifically, Table <NUM> of <FIG> shows ductility test results for the self-drilling self-tapping fastener <NUM> of <FIG> in comparison to six example commercially available self-drilling self-tapping fasteners. Table <NUM> shows that the ductility of the fastener <NUM> is not different than the ductility of the six commercial fasteners. It should be appreciated that suitable fastener ductility is necessary to avoid hydrogen embrittlement failure, hydrogen assisted stress corrosion failure, and the effects of thermal expansion and contraction of the objects in which the fastener is tapped, fastened, and secured. It should be also be appreciated that industrial standards use suitable bend tests to evaluate a fastener's ductility. As shown in Table <NUM> of <FIG>, the tests used to test the ductility of the fasteners tested was a <NUM> degree head bend test, and. five samples of each fastener were tested. All samples passed the <NUM> degree bend test except the Fastener-D sample. The failure appears to be due to such fasteners having a higher core hardness and a deeper case. It should thus be appreciated that core hardness and case depth are the two more important factors that determine the fastener's ductility.

Table <NUM> of <FIG> shows torsional strength vs root diameter test results for the self-drilling self-tapping fastener <NUM> of <FIG> in comparison to six commercially available self-drilling self-tapping fasteners. Table <NUM> shows that the torsional strength of the fastener <NUM> has the best torsional strength comparing to six commercial fasteners except the Fastener-D sample. It should be appreciated that in addition to material and heat treating, root diameter is one of the more important factors that determines a fastener's torsional strength (i.e., typically, the larger of root diameter, the higher of the torsional strength). It should also be appreciated that, as shown in Table <NUM>, the root diameter of Fastener-B, Fastener-A, and Fastener-F are <NUM>%, <NUM>%, and <NUM>% of the fastener <NUM>, respectively, so their respective torsional strengths are lower than that of the fastener <NUM>, and only <NUM>%, <NUM>%, and <NUM>% of the fastener <NUM>. It should also be appreciated that the Fastener-D has the highest torsional strength, not only because its root diameter is similar (<NUM>%) to the fastener <NUM>, but also because it has the highest core hardness. It should be appreciated that higher core hardness will provide higher torsional strength, but high core hardness will reduce fastener's ductility as mentioned above regarding ductility. Fastener-A has a similar root diameter as fastener <NUM>, so it has a good optimum balance of tensile strength and ductility. To reach the optimum balance of ductility and torsional strength, fastener <NUM> has a root diameter in the range of <NUM>-<NUM> inches (<NUM> to <NUM> cms).

Table <NUM> of <FIG> shows tensile strength vs root diameter test results for the self-drilling self-tapping fastener <NUM> of <FIG> in comparison to six commercially available self-drilling self-tapping fasteners. Table <NUM> shows that the fastener <NUM> has the best tensile strength comparing to six commercial fasteners. It should also be appreciated that in addition to material and heat treating, root diameter is the more important factor that determines fastener's tensile strength (e.g., generally the larger the root diameter, the higher of the tensile strength). As Table <NUM> shows, the root diameter of Fastener-B, Fastener-A, and Fastener-F are <NUM>%, <NUM>%, and <NUM>% of the fastener <NUM>, respectively, so their respective tensile strengths are lower than the fastener <NUM>, and only <NUM>%, <NUM>% and <NUM>% of the fastener <NUM>. On the other hand, Fastener-A has a similar root diameter as fastener <NUM>, so it also has a comparable tensile strength. To reach the best performance of fastener tensile strength, the fastener <NUM> has a root diameter in the range of <NUM> to <NUM> inches (<NUM> to <NUM> cms).

Table <NUM> of <FIG> shows pullout vs thread engagement test results for the self-drilling self-tapping fastener <NUM> of <FIG> in comparison to six commercially available self-drilling self-tapping fasteners. If fastener material, heat treatment, and thread profile are the same, screw thread engagement with the substrate, or the difference of thread OD and drill point OD, appears to be the more important factor that determines the fastener pullout value from the substrate (e.g., the larger the difference, the higher of the pullout value). However, the larger the difference, the harder it is for the threads to tap into the substrate, and thus the higher the tapping torque. Table <NUM> shows that the fastener <NUM> has the best pullout performance, followed by Fastener-A and Fastener-D that respectively have <NUM>% and <NUM>% of the pullout value of Fastener <NUM>. Fastener-D has <NUM>% of thread engagement of fastener <NUM>, so it has <NUM>% of the pullout value of fastener <NUM>. Fastener-A has a little larger thread engagement (<NUM>%) than fastener <NUM>, but a little lower pullout force (<NUM>%) than fastener <NUM> because Fastener-A has a larger point eccentricity, so the actual hole size Fastener-A drilled is larger than the point OD, which reduced its pullout value. Fastener-B, Fastener-C, Fastener-A, and Fastener-F have much lower pullout values (<NUM>%, <NUM>%, <NUM>%, <NUM>%, respectively) since their thread engagements are also smaller (<NUM>%, <NUM>%, <NUM>%, <NUM>% compared to fastener <NUM>). Table <NUM> thus shows that the pullout force of the fastener <NUM> is significantly higher than the pullout force of each of the six commercial fasteners. It should be appreciated that if the fastener material, heat treatment, and thread profile are the same, the thread engagement with the steel object or the difference of thread OD and drill point OD thus appear to be the more important factor(s) that determine the fastener pullout value from an object (e.g., generally the larger of the difference the higher of the pullout value). It should further be appreciated that the larger the difference, the harder for the threads to tap into the object(s), or the higher the tapping torque will be. It should also be appreciated from Table <NUM> that the fastener <NUM> has the best pullout value in part due to the thread engagement of around <NUM> inches (<NUM> cms). To reach the best pullout performance and a reasonable drill tapping torque, the fastener <NUM> has a thread engagement in the range of <NUM> to <NUM> inches (<NUM> to <NUM> cms), and the drill point eccentricity is less than <NUM> inches (<NUM> cms). It should be appreciated that this drill point eccentricity may be achieved via forging the second shank portion <NUM> or by milling this second shank portion with tight manufacturing tolerances.

It should further be appreciated that to reach the best pullout performance and at the same time to keep the tapping torque at a reasonable low level, the fastener <NUM> has a second shank portion <NUM> with the combination of the chip breakers and the thread formation <NUM> with only <NUM> threads at the flute transition section on one side of the fastener <NUM>.

Table <NUM> of <FIG> shows drilling time/torque vs point geometry test results for the self-drilling self-tapping fastener <NUM> of <FIG> in comparison to six commercially available self-drilling self-tapping fasteners for both tests on <NUM>/<NUM> inch thick steel plate and ½ inch thick steel plate,. As mentioned above, Table <NUM> shows that the drilling time of the fastener <NUM> is significantly lower than the drilling times of each of the six commercial fasteners. These comparisons show that drill point geometry is an important factor that determines drilling time. Generally, the sharper the drill point is, the faster it can drill into a steel substrate, and the less drilling time is needed to drill through the steel substrate. However, since the self-drilling self-tapping fastener <NUM> must be able to drill through at least ½ inch thick steel plate, if the drill point is too sharp, it will be worn easily, and then cannot drill through such substrate or may need more time to do so. Thus, the drill point sharpness of the fastener <NUM> appears to be important in obtaining this lowest drilling time. The fastener <NUM> has a cutting edge center distance in the range of <NUM> inches to <NUM> inches, a drill point web thickness in the range of <NUM> inches to <NUM> inches, and a point cutting edge angle in the range of <NUM> to <NUM> degrees. These features appear to provide the fastener <NUM> with this significantly lower drilling time. It should be appreciated from the above that the fastener <NUM> has: (<NUM>) an improved performance in drilling time and specifically a relatively lower drilling time, and (<NUM>) an improved performance in pullout force and specifically a relatively higher pullout force, all without decreasing performance in any of the comparative ductility, tapping torque, torsional strength, or tension strength of the fastener <NUM>, when compared to various known commercially available self-drilling self-tapping fasteners of the similar size and form.

It should be appreciated that the above dimensions are subject to reasonable variation due to manufacturing tolerances in accordance with the present disclosure. It should also be appreciated that the above dimensions are based on actual measurements and thus take into account manufacturing tolerances. It should further be appreciated that the actual designed dimensions may be different and result in such actual manufacturing tolerances in accordance with the present disclosure.

In further embodiments of the present disclosure, the fastener length may vary. In one example alternative embodiment, the fastener is a #<NUM>-<NUM> x <NUM>-<NUM>/<NUM> inch fastener and is ¼ inches longer than fastener <NUM>. In another example alternative embodiment, the fastener <NUM> is a #<NUM>-<NUM> x <NUM>-<NUM>/<NUM> inch fastener and is <NUM>/<NUM> inches longer than fastener <NUM>. In another example alternative embodiment, the fastener <NUM> is a #<NUM>-<NUM> x <NUM> inch fastener and is <NUM>/<NUM> inches longer than fastener <NUM>. In these example alternative embodiments, the respective thread lengths have increased by a ¼ inch, a ½ inch, and ¾ inches for each of above respective fasteners, but the other dimensions are identical.

Claim 1:
A self-drilling self-tapping fastener (<NUM>) comprising:
a head (<NUM>);
a shank (<NUM>) integrally connected to and extending from the head, the shank including a first shank portion (<NUM>) and a second shank portion (<NUM>), the second shank portion defining a longitudinally extending first flute (<NUM>), the second shank portion defining a longitudinally extending second flute (<NUM>), the second shank portion including a first chip breaker (<NUM>) positioned in the first flute, the second shank portion including a second chip breaker (<NUM>) positioned in the second flute, the second shank portion including a drill tip (<NUM>), the drill tip including a first cutting blade (<NUM>) having a first cutting edge (<NUM>) and a second cutting blade (<NUM>) having a second cutting edge (<NUM>), wherein the first cutting edge and the second cutting edge are tapered toward each other; and
a helical thread formation (<NUM>) integrally connected to and extending radially outwardly from the first shank portion and part of the second shank portion,
characterized in that the first flute (<NUM>) extends through three threads of the thread formation (<NUM>) on a first side of the second shank portion (<NUM>), but not to the fourth thread on the first side of the second shank portion.