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FIELD OF THE INVENTION 
     This invention relates generally to framing members and, more specifically, to small, lightweight framing members which can be conveniently used to assemble work benches, storage shelves, bookcases, etc. 
     BACKGROUND OF THE INVENTION 
     Small lightweight prefabricated framing members have become increasingly popular in the construction of industrial equipment, such as tooling, machinery, conveyors and robotic enclosures. A typical such framing member is made from an aluminum alloy and has a configuration which makes it versatile in constructing fixtures and furniture. The framing member has a square cross-section. On each of the four sides of the framing member, an elongate groove is defined. The elongate groove has a pair of opposed interior shoulders. The elongate grooves are designed to accept attachment bolts. The attachment bolts are attached to attachment nuts disposed within the grooves. When each bolt is tightened, its attachment nut impinges upon the underside of the interior shoulders of the groove, thereby firmly retaining the attachment nut within the groove. 
     There is a problem, however, with framing members having such grooves. That problem arises from the fact that it can be very difficult to position the attachment nut within the groove and thread the attachment bolt into the attachment nut. Moreover, if the attachment nut is positioned behind a bracket or other large object, the attachment nut can be very difficult to see within the groove during the threading of the attachment bolt into the attachment nut. 
     Accordingly, there is a need for a lightweight framing member which avoids these problems in the prior art. 
     SUMMARY OF THE INVENTION 
     The invention satisfies this need. The invention is a framing member comprising an elongate body having at least one elongate U-shaped trough defined by a bottom wall and a pair of opposed side walls, the pair of opposed side walls both having a plurality of linear side wall grooves running continuously substantially along the entire length of the U-shaped trough, each side wall groove being defined by a plurality of side wall protuberances, a plurality of the side wall protuberances having squared off edges. 
     The invention is also a combination of the framing member described above and a fastener screw having threads with squared off edges. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims and accompanying drawings where: 
     FIG. 1 is an isometric view of a framing member having features of the invention; 
     FIG. 2 is a cross-sectional view of the framing member illustrated in FIG. 1, shown in combination with a fastener screw; 
     FIG. 3 is a detail view of a cross-section of the attachment member illustrated in FIG. 1; 
     FIG. 4 is a detail view of a fastener screw having features of the invention; 
     FIG. 5 is a detail view showing the attachment of the attachment screw illustrated in FIG. 1; 
     FIG. 6 is an end view of the attachment member illustrated in FIG. 1 shown in combination with three different accessory pieces; 
     FIG. 7 is a end view of a pair of framing members, such as illustrated in FIG. 1, shown connected by a pair of sliding doors; 
     FIG. 8 is an end view of a first industrial cabinet constructed with the framing member illustrated in FIG. 1; 
     FIG. 9 is a front view of a second industrial cabinet constructed with the framing member illustrated in FIG. 1; and 
     FIG. 10 is a perspective view of a pair of framing members having features of the invention. 
    
    
     DETAILED DESCRIPTION 
     The following discussion describes in detail one embodiment of the invention and several variations of that embodiment. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. 
     The invention is a framing member  10  having an elongate body with at least one U-shaped trough  12 . The U-shaped trough  12  is defined by a bottom wall  14  and a pair of opposed side walls  16 . The pair of side walls  16  have a plurality of opposed elongate linear side wall grooves  18  running continuously substantially along the entire length of the U-shaped trough  12 . Each side wall groove  18  is defined by a plurality of elongate side wall protuberances  20 . In the invention, a plurality of the side wall protuberances  20  have squared off edges  22 . The term “squared off edges,” when used with respect to the side wall protuberances  20 , is intended to mean that the edges  22  of the side wall protuberances  20  form an angle of between about 85° and about 95°, typically about 90°. 
     Typically, the framing member  10  can be made from an aluminum alloy, but other materials can also be used, such as other metals and plastics. 
     In the embodiment illustrated in the drawing, the framing member  10  comprises a central portion  24  and four elongate U-shaped troughs  12  radially extending away from the central portion  24 . Each U-shaped trough  12  is disposed 90° apart from each adjoining U-shaped trough  12 . Each of the U-shaped troughs  12  has a plurality of linear side wall grooves  18  running continuously along substantially the entire length of the U-shaped trough  12 . Each side wall groove  18  is defined by a plurality of side wall protuberances  20 , a plurality of the side wall protuberances  20  having squared off edges  22 . 
     Also in the embodiment illustrated in the drawings, the framing member  10  comprises four elongate diagonal plates  26 . Each diagonal plate  26  extends away from the central portion  24 . Each diagonal plate  26  is disposed between an adjoining pair of U-shaped troughs  12 . In the embodiment illustrated in the drawings, each diagonal plate  26  is disposed apart from each adjoining U-shaped trough  12  by identical angles α of 45°. The diagonal plates  26 , however, can be disposed with respect to adjoining U-shaped troughs  12  at other angles α as well. 
     In the embodiment illustrated in the drawings, each diagonal plate  26  has an end member  28  with two end portions  30  disposed at 90° with respect to one another, so that the end member  28  has an arrow-shaped cross-section. The two end portions  30  of the end member  28  lie in perpendicular planes which are both parallel to the side walls  16  of two of the U-shaped troughs  12 . The length of each end portion  30  of the end member  28  determines the distance between each end portion  30  and a line  32  extending away from the nearest side wall  16  of a U-shaped trough  12 . This distance is typically predetermined to provide a convenient attachment opening  34  for a construction sheet  36 , such as a plywood or Masonite sheet, having a standard thickness which corresponds to the width of the attachment opening  34 . The use of the attachment opening  34  to accept and retain a construction sheet  36  is illustrated in FIG.  6 . 
     As also illustrated in FIG. 6, the space between opposed end portions  30  of two adjoining end members  28  can be capped by a slat  38  of corresponding width. 
     As illustrated in FIG. 3, the side wall protuberances  20  in each U-shaped trough  12  are staggered to form an attachment location  40  for a threaded screw  42 . In a typical embodiment, wherein the height a of each U-shaped trough side wall  20  is about 0.500 inches, the distance b between the side wall protuberances  20  in each U-shaped trough  12  is typically between about 0.060 inches and about 0.070 inches, most typically about 0.065 inches, except that the depth c of the initial notch  44  on the right side of the U-shaped trough  12  in FIG. 3 is typically between about 0.0450 inches and about 0.0550 inches, most typically about 0.0500 inches. The width d of each side wall protuberance  20  in each U-shaped trough  12  is typically between about 0.04 inches and about 0.05 inches, most typically about 0.045 inches, except that the width e of the initial side wall protuberance  12   i  on the left side of the U-shaped trough  12  illustrated in FIG. 3 is typically between about 0.025 inches and about 0.035 inches, most typically about 0.030 inches. The length f of each side wall protuberance  20  is typically between about 0.140 inches and about 0.150 inches, most typically about 0.145 inches. The overall width g of the U-shaped trough  12  is typically between about 0.480 inches and about 0.500 inches, most typically about 0.490 inches. The distance h between the opposed side walls  16  of the U-shaped trough  12  is typically between about 0.190 inches and about 0.210 inches, most typically about 0.200 inches. 
     The framing member  10  is preferably used with threaded fastener screws  42  having threads  46  with squared off edges  48 , as illustrated in FIG.  4 . The term “squared off edges,” when used with respect to the fastener screws  42 , is intended to mean that the outer edges  48  of the threads  46  are disposed substantially parallel to the longitudinal axis  50  of the screw  42 . Thus, the outer edges  48  of each thread  46  form angles which are approximately 90°, but are not exactly 90°. 
     The threads  46  of the fastener screw  42  are sized and dimensioned such that, when the fastener screw  42  is disposed within one of the U-shaped troughs  12  of the framing member  10 , the threads  46  of the fastener screw  42  are disposed proximate to the base portion  52  of the side wall protuberances  20  and are disposed proximate to the squared off edges  22  of the side wall protuberances  20 , but do not adversely effect the squared off edges  22  at the apex portion  53  of the side wall protuberances  20 . This is illustrated in FIG. 5 where it can be seen that each of the threads  46  of the fastener screw  42  is disposed deeply within each of the grooves  18  between the side wall protuberances  20  and each of the threads  46  is disposed proximate to the squared off edges  22  of the side wall protuberances  20 , but none of the threads  46  of the fastener screw  42  impinge upon the squared off edges  22  of the side wall protuberances  20  to such an extent that the side wall protuberances  20  are deformed with respect to their squared off configurations. 
     A typical fastener screw  42  for use with a framing member  10  comprises side walls and with a height a of about 0.500 inches is a screw  42  having threads  46  which have a thickness i which is typically between about 0.035 inches and about 0.045 inches, most typically about 0.040 inches. The threads  46  are typically spaced apart by a distance j of between about 0.0700 inches and about 0.0750 inches, most typically about 0.0725 inches. The threads  46  protrude away from the central member  54  of the fastener screw  42  by a distance k typically between about 0.0600 inches and about 0.0625 inches, most typically about 0.06125 inches. The diameter  1  of the central member  54  of the fastener screw  42  is typically between about 0.180 inches and about 0.200 inches, most typically about 0.190 inches. The diameter m of the threads  46  is typically between about 0.3000 inches and about 0.3250 inches, most typically about 0.3125 inches. The head  56  of the fastener screw  42  typically has a height n of between about 0.165 inches and about 0.1875 inches. 
     In most preferred embodiments, the threads  46  of the fastener screw  42  have a thickness i, a distance between adjoining threads j and j/i is between about 1.5 and about 2.0, most preferably between about 1.7, and about 1.9. 
     In a typical fastener screw  42  having a nominal outside diameter of {fraction (5/16)} inch, the fastener screw  42  has nine threads per inch, a pitch of 0.1105 inches and a helix angle (the angle of the threads with respect to the horizontal) of 8.104°. The angle at which each thread  46  meets the central member  54  of the screw  42  is nearly 90°, typically between about 85° and about 90°, and most typically about 88°. Thus, the “flank angle” of the screw  42  is between about 0° and about 5°, typically about 2°. 
     In a typical embodiment, the fastener screw  42  is made from steel, although other materials, such as other metals and plastics, can also be used. 
     As illustrated in FIG. 6, each of the U-shaped troughs  12  can be capped by a elongate channel member  58 . 
     As illustrated in FIG. 7, a decorative cap trim element  60  can be disposed between opposed end portions  30 . Also, an optional glazing seal strip  62  can be conveniently added for clean environments. Finally, as illustrated in FIG. 7, easy to install, snap-in sliding door guides  64  can be used to retain a pair of sliding doors  66 . 
     FIGS. 8 and 9 illustrate two different items of industrial furniture  68  capable of easily assembly using the framing member  10  of the invention. Brackets  70  are used to support the several framing members  10  using attachment screws  42  disposed within the U-shaped troughs  12 . 
     FIG. 10 illustrates a very important feature of the invention. In the invention, once the fastener screws  42  are fully disposed within a U-shaped trough  12 , but before the fastener screw  42  is finally tightened within the U-shaped trough  12 , the fastener screw  42  can freely travel within the U-shaped trough  12 . This is because the threads  46  of the fastener screw  42  do not rigidly contact the side wall protuberances  20  until the fastener screw  42  is finally tightened within the U-shaped trough  12 . After the fastener screw  42  is fully disposed within the U-shaped trough  12 , but before the fastener screw  42  is finally tightened within the U-shaped trough  12 , there is sufficient clearance between the threads  46  of the fastener screw  42  and the side wall protuberances  20  to allow the fastener screw  42  to freely be slid back and forth within the U-shaped trough  12 . This important feature makes it easy for the user to properly align contiguous framing members  10  with respect to one another. For example, in the embodiment illustrated in FIG. 10, the framing member  10   a  can be easily aligned with respect to the framing member  10   b  by disposing a threaded screw  42   a  into the connecting bracket  70   a  and fully disposing the fastener screw  42   a  within the U-shaped trough  12   b  of the framing member  10   b . Then the bracket  70   a , the fastener screw  42   a  and the framing member  10   a  can be moved back and forth with respect to framing member  10   b  until the framing member  10   a  is perfectly aligned with respect to framing member  10   b . At that point, the alignment can be secured by finally tightening the fastener screw  42   a  within the U-shaped trough  12   b  of the framing member  10   b.    
     The invention provides a framing member which is inexpensive but is versatile and durable. The framing member does away with the need to position a fastener nut within the groove disposed within the framing member. Because of the unique construction of the framing member, the framing member can be used over and over again without damage to the attachment sites within the U-shaped troughs. When used in combination with the steel screws having squared off threads and when the design and dimensions of the side wall protuberances match the threads of the attachment screws as described herein, the attachment screw does no damage to the side wall protuberances. Thus, the attachment screw can be inserted and withdrawn at the same location without damaging the framing member. 
     Having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims.

Summary:
A framing member has an elongate body with at least one elongate U-shaped trough. The side walls of the U-shaped trough define a plurality of elongate side wall protuberances having squared off edges. The framing member can be used with a fastener screw having squared off edges to assemble commercial and residential work benches, storage shelves, bookcases, etc.