2. Description of the prior art The art of fasteners, including screws, has been well developed over the years. For instance, United States Patent No. 4,241,638 issued to Shimizu et al. on December 30,1990 discloses a self- extruding fastener having an externally threaded stem having defining two screw threads which helically extend in a substantially parallel and alternate relationship around the stem. The fastener is provided at its distal end with a tapering portion terminating with a sharp pointed forward end adapted to form a guide hole in a thin sheet of metal. A third screw thread generates in a position mid-way between the first two screw threads and substantially where the stem ends and the tapering portion begins with this third screw thread extending to the pointed forward end while the first two screw threads disappear in the tapering portion. The pointed end allows the fastener to extend through a metal stud made of a thin sheet of metal located behind a conventional plaster board such as to ultimately secure the latter to the metal stud.

U. S. Patent No. 5,569,009 issued to Suzuki on October 29,1996 discloses a loosening prevention screw for fastening various materials and reliably prevent the loosening of the screw. The screw shank is thus formed with two threads, namely a main thread for driving the screw and a sub-thread which helically extends in the same direction as the main thread, alternating therewith, and which is smaller in its outer diameter than that of the main thread and which has a pitch which is different from the main thread. The inclination of the slant surface of the sub-thread is set steep on the loosening side and moderate on the fastening side with the pitch of the main thread being larger than that of the sub-thread.

Therefore, when the tightened screw is applied a loosening torque, the sub-thread bites into the inner wall of the hole thereby preventing the screw from loosening.

United States Patent No. 3,207,023 issued to Knohl on September 21,1965 discloses a screw fastener having a pair of helically wound threads which extend substantially parallelly to each other and in an alternating way, both threads having substantially the same pitch but with one thread having a relatively greater height than the other.

European Patent Publication No. EP-0 281 203-A1 published on September 7,1988 in the name of Kilton S. R. L. discloses a self-tapping screw for high speed tools which has a cylindrical stem followed by a conical tip with the thread extending right to the tip of the screw with an intermediate smaller thread also extending on the tip of the screw and helically parallelly between the main thread.

British Patent Publication No. GB-2 070 996-A published on September 16,1981 in the name of Illinois Tool Works Inc. discloses a self-drilling and self-tapping screw which has a pair of alternating helically wound threads in a way similar to that of the aforementioned of U. S. Patent No.

3,207,023.

West German Patent Publication No. DE-28 53 976-A1 published on June 19,1990 in the name of Eberhard Jaeger GmbH & Co. KG discloses a self- tapping screw having a main shank with a constant diameter external thread and a boring tip having a proximal parallel or cylindrical portion and a distal tapering pointed tip, the boring tip being also threaded but with a thread having a smaller diameter and a smaller pitch than that of the thread of the main shank.

West German Patent Publication No. DE-30 03 280-A1 published on August 6,1981 to Knoche discloses a self-tapping screw provided with twin threads with identical pitches but with different thread thicknesses and with both threads alternating with one another along the stem of the screw.

SUMMARY OF THE INVENTION It is therefore an aim of the present invention to provide a novel screw.

It is a further aim of the present invention to provide a hybrid screw.

It is a further aim of the present invention to provide a hybrid screw having a pair of consecutive threads suited for engagement with different types of materials.

It is a still further aim of the present invention to provide a screw having a side opening in its stem and located in a proximally spaced apart relationship to a tip of the screw.

Therefore in accordance with the present invention, there is provided a fastener comprising an elongated body having opposed first and second ends and stem means therebetween, said first end being adapted to be engaged by a rotatable tool to rotate said fastener about a longitudinal axis thereof and to cause it to gradually engage at least one material, said second end being adapted to cut through said material as said fastener is rotated, said elongated body defining first and second external thread means provided substantially around said stem means and said second end respectively, said first and second thread means being suited to engage two substantially different materials.

Typically, said first thread means has successive apexes which decrease at a larger rate than apexes of the second thread means. More particularly, for first and second imaginary lines which respectively join said apexes of said first and second thread means, a first angle of said first imaginary line with respect to the vertical being significantly greater than a second angle of said second imaginary line with respect to the vertical.

Also in accordance with the present invention, there is provided a fastener comprising an elongated body having head means and stem means extending therefrom, said head means being adapted to be engaged by a rotatable tool to rotate said fastener about a longitudinal axis thereof and to cause it to gradually engage at least one material, said stem means being adapted to cut through said material as said fastener is rotated and defining external thread means, said stem means defining an inner cavity and a side opening communicating with said inner cavity for assisting in the evacuation of material cut by said fastener during rotation thereof, said side opening being spaced from a distal end of said fastener.

BRIEF DESCRIPTION OF THE DRAWINGS Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: Figure 1 is a front elevational view of a hybrid screw in accordance with the present invention; Figure 2 is a side elevational view of the hybrid screw of Figure 1, taken at a 90° angle with respect to the position of Figure 1; Figure 3 is a top plan view of the hybrid screw; Figure 4 is front elevational view of another embodiment of a hybrid screw in accordance with the present invention; Figure 5 is a side elevational view of the hybrid screw of Figure 4, taken at a 90° angle with respect to the position of the screw in Figure 4; Figure 6 is a top plan view of the hybrid screw of Figures 4 and 5; Figure 7 is a perspective view of a third embodiment of a hybrid screw in accordance with the present invention; Figure 8 is a side elevational view of the hybrid screw of Fig. 7; Figure 9 is a side elevational view of the hybrid screw of Figure 7, taken at a 90° angle with respect to the position of the screw in Figure 8; and Figure 10 is a top plan view of the hybrid screw of Fig. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring mainly to Figure 1, there is shown a hybrid screw S in accordance with the present invention, wherein the screw has a flared head 10 merging with a cylindrical stem 12 which itself merges with a distal pointed section 14.

The head 10 defines a cruciform opening 16 adapted to be engaged by a conventional star- shaped (i. e. Phillips) screwdriver head such that rotation of the screwdriver about its longitudinal axis will cause the screw S to rotate similarly.

The cruciform opening 16 communicates with an inner bore 18 defined in the cylindrical stem 12.

The cylindrical stem 12 further defines on its side wall an opening 20 which communicates with the inner bore 18. The inner wall of the cylindrical stem 12 which defines the inner bore 18 is provided with four longitudinal ribs or splines 19, as best seen in Figure 3.

The hybrid screw S is provided externally thereof with a continuous thread 22 which includes a first thread section 24 extending generally around the cylindrical stem 12, and a second thread section 26 extending generally around the distal pointed section 14.

Both the first and second thread sections 24 and 26 have substantially the same pitch in order to maintain constant the rate of advancement of the hybrid screw S, per rotation thereof, in the material even when both thread sections 24 and 26 are engaged therein.

The first thread section 24 is large and thus well suited for securing the hybrid screw S in a friable material, such as gypsum walls. The second thread section 26 and its pointed tip 28 are capable of cutting a hole through the gypsum wall which is then enlarged by the cylindrical stem 12 with the first thread section 24 thereof compacting the gypsum material and firmly securing the hybrid screw S to the gypsum wall. The side opening 20 allows for the wall material cut by the hybrid screw S during the rotation thereof to enter the inner bore 18 such as to evacuate these fragments from the opening being cut in the wall.

The present hybrid screw S can be used, for instance, to secure objects, such as picture frames to gypsum walls. Various gypsum wall screws have been developed over the years which, as with the first thread section 24 of the present hybrid screw S, are provided with large threads which cause the wall material to sufficiently compact around the screw such as to firmly secure the same to the wall. Furthermore, the screws of the prior art, in a way similar to the present hybrid screw S, are longer than the thickness of the gypsum board of the wall and thus protrude from the gypsum board, inside the wall. If the screw is engaged in the wall opposite a stud thereof, such as a wooden structural 2"x 4' board, a typical gypsum wall screw will not properly engage the wooden stud and the rate of translational advancement of the screw will be reduced thereby causing the thread of the screw to destroy the female thread formed thereby in the gypsum, whereby the screw will become loose.

In the present invention, the distal pointed section 14 is of relatively smaller transverse dimension than that of the cylindrical stem 12 and, in a way similar to a conventional wood screw, is capable of easily engaging a wooden member without reduction of the rate of advancement of the hybrid screw S, per rotation thereof. In other words, if the hybrid screw S is engaged into a gypsum wall at a location where it will, when extending through the gypsum wall, engage a wooden stud, the distal pointed section 14 and its second thread section 26 will be able to threadably engage the wooden stud without hampering the rate of advancement of the hybrid screw S through the gypsum wall S thereby avoiding the large first thread section 24 from destroying the female thread in the friable material of the wall which is the case if it rotates without simultaneously translationally advancing as per its pitch. Once the flared head 10 lies coplanar with the outside surface of the wall, the second thread section 26 is at least mostly engaged in the wood member, whereas the first thread section 24 is at least mostly engaged in the gypsum wall, whereby the hybrid screw S is firmly secured to the wall. If there are no wooden studs behind the gypsum wall, the engagement of the first thread section 24 with the gypsum wall is sufficient to firmly secure the hybrid screw S to the wall.

Therefore, the present hybrid screw S can be firmly secured to a gypsum wall whether or not it is engaged opposite a hidden structural wooden member.

The present hybrid screw S could be designed such that, once installed in the wall, it can receive in its inner bore 18 a further threaded fastener, such as a solid screw, which, as it is rotated into the inner bore 18 taps a female thread in the splines 19 such as to become firmly secured to the hybrid screw S. The head of such a screw engaged in the hybrid screw S is typically left in a spaced apart relationship with respect to the wall and the flared head 10 of the hybrid screw S such that a cable or other can be engaged on the screw between its head and the head 10 of the hybrid screw S. The engagement of such an additional fastener to the hybrid screw S of the present invention is well known in the art and reference is made to United States Patents No.

1,051,444 and No. 1,248,008 both issued to Pleister on January 28,1913 and November 27, 1917, respectively, and also to U. S. Patent No.

4,601,625 issued to Ernst et al. on July 22,1986.

Figures 4 to 6 illustrate another hybrid screw S'in accordance with the present invention which is similar to the hybrid screw S of Figures 1 to 3 although it is exempt of the side opening 20 found in the hybrid screw S of Figures 1 to 3.

Typically, in the hybrid screw S', the second thread section 26'has a pitch essentially similar to that of the first thread section 24'for the reasons set forth hereinabove in the description of the hybrid screw S.

Again, it must be noted that in prior art screws defining large threads for firmly engaging the friable material of a gypsum wall, such as those of the first thread section 24 of the present hybrid screw S, the prior art large threads extend for a length largely exceeding the thickness of the gypsum wall and typically for the combined length of the thread 22 of the present screw. In such prior art cases, if the conventional screw encounters a two by four wood member, its large gypsum-wall designed thread is inadequate to penetrate the wooden member and this causes the screw to spin and to thus destroy the female threads defined previously thereby in the gypsum wall.

It is again also noted that the pitches of both the first and second thread sections 24 and 26 of the present hybrid screw S are identical such that when the second thread section 26 engages a wooden component, its axial advancement per rotation of the screw is identical to that of the first thread section 24 in the gypsum wall thereby ensuring that the first thread section 24 does not itself destroy the female thread defined thereby in the gypsum wall.

Both the hybrid screws or anchors S and S'are provided on the first and second thread sections 24/24'and 26/26'with anti-loosening notches 30 and 30', respectively, which assist in preventing the screw S/S'from becoming disengaged from the wall.

In Figs. 7 to 10, there is shown a third hybrid screw S"which includes a flared head 10", a stem 12", a cruciform opening 16"for engagement by a screwdriver-like tool, and a thread 22" provided helically around the stem 12"and comprising first and second thread sections 24" and 26", respectively. The stem 12"terminates with a distal pointed section 14". The thread 22" of the screw S"is similar to the threads 22 and 22'respectively of screws S and S'in that it has dimensions suited for fixedly engaging different types of materials, such as gypsum and wood respectively for the first and second thread sections 24"and 26".

The first thread section 24"has successive apexes which decrease at a larger rate than apexes of the second thread section 26", as seen in Fig. 9 by imaginary lines 32 and 34 which respectively join apexes of the first and second thread sections 24"and 26". The angle of line 32 with respect to the vertical is significantly greater than that of the line 34.

It must be noted that the screw S"of Figs. 7 to 10 is not provided with an inner bore, such as the evacuation inner bore 18 of the anchors S and S'of Figs. 1 to 6. The screw S" however remains a screw which can be engaged in two different materials but which is not adapted to evacuate or receive materials cut from the wall, as in the embodiments of Figs. 1 to 6, nor is it adapted to subsequently receive therein a further threaded fastener, as variants of the embodiments of Figs. 1 to 6 could.