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CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of application Ser. No. 15/080,506, filed 24 Apr. 2016, which is a continuation-in-part application of application Ser. No. 14/678,644, filed 3 Apr. 2015, which in turn claims the benefit of, and priority to, U.S. Provisional Application No. 61/974,676 filed on 3 Apr. 2014, and U.S. Provisional Application No. 62/137,681 filed on 24 Mar. 2015, all incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to modular assembly systems. More particularly, the present invention relates to modular assembly systems for office and industrial work stations. 
     BACKGROUND 
     Modular building assembly systems have long been available to for the construction and erection of various structures such as office cubicles, industrial work stations, and scaffolding. Such modular building assembly systems usually have some type of standard beam that can be joined to other beams and to which various accessories can be attached. Solid bars, of circular or regular polygonal shape (such as square or hexagonal) may be used, but are inferior to tubes of the same shape because tubes have a better resistance to torsion for the same mass of material than do solid bars. Circular or regular polygons lack an easy point of attachment for accessories and other beams, so more complex shapes are preferred. One such complex shaped beam is a cruciform beam (see U.S. Pat. No. 5,481,842 to Gautreau, FIG. 1). The cruciform beam comprises a center tube surrounded by four angle bars arranged in a square pattern in cross-section and each joined to the center tube with a web or fin, the fins forming a cross when the beam is viewed in cross-section. Accessories can be attached along the cruciform beam by clamping the accessory to one of the angle bars or in a longitudinal groove defined by the spaces between the fins and angle bars. The cruciform beam is relatively strong in resisting buckling when torsion is applied to the beam around an axis orthogonal to the long axis of the cruciform beam because in cross-section, a substantial amount of the beam material is distant from the center longitudinal axis. Such torsion occurs when the cruciform beam spans a space and a load is attached to the beam somewhere in the middle. However, the cruciform beam is not relatively strong when torsion is applied around the long axis of the cruciform beam. Such torsion occurs when a load is cantilevered from the side of the cruciform beam. Since a cruciform beam for a given size and weight does not have good resistance to torsion around its long axis, accessories are usually not cantilevered from the side of the cruciform beam. 
     What is needed is a modular building system with a beam that has strong resistance to torsion around its long axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
       The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the detailed description, serve to explain the principles and implementations of the invention. 
         FIG. 1  is a perspective view of a first embodiment of a quad-track beam. 
         FIG. 2  is a perspective view of a strut nut and a portion of a channel leg. 
         FIG. 3  is a perspective view of a second embodiment of a quad-track beam. 
         FIG. 4 a    is a top view of a straight configuration quad-track beam. 
         FIG. 4 b    is a top view of a diamond configuration using quad-track beams. 
         FIG. 4 c    is a top view of a cross configuration using quad-track beams. 
         FIG. 4 d    is a top view of a star configuration using quad-track beams. 
         FIG. 5 a    is a top view of a joint in the star configuration. 
         FIG. 5 b    is a top view of a joint in the diamond configuration. 
         FIG. 6 a    is a perspective view of a single channel leg. 
         FIG. 6 b    is a cross-section view of a single channel leg from the top. 
         FIG. 6 c    is a cross-section view of an alternative single channel leg from the top. 
         FIG. 6 d    is a cross-section view of a double channel leg from the top. 
         FIG. 7  is a perspective view of an application using quad-track beams. 
         FIG. 8  shows a third embodiment of a quad-track beam. 
         FIG. 9A  shows a fourth embodiment of a quad-track beam in a perspective view. 
         FIG. 9B  shows an exploded perspective view of the fourth embodiment quad-track beam. 
         FIG. 9C  shows the fourth embodiment quad-track beam in a perspective view with components for attaching accessories. 
         FIG. 10A  shows a top view of a first embodiment of a dual quad-track beam assembly. 
         FIG. 10B  shows a perspective view of a dual beam brace bracket. 
         FIG. 11A  shows a perspective view of a second embodiment of a dual quad-track beam assembly. 
         FIG. 11B  shows a top view of the second embodiment of a dual quad-track beam assembly. 
         FIG. 12  shows a perspective view of a first embodiment of a dual quad-track beam cruciform module. 
         FIG. 13A  shows a perspective view of a second embodiment of a dual quad-track beam cruciform module. 
         FIG. 13B  shows a perspective view of a central mounting plate. 
         FIG. 14A  shows a perspective view of a dual quad-track beam assembly with cantilevered legs attached, forming a first exemplary workstation arrangement. 
         FIG. 14B  shows a top view of the leg mounting plate. 
         FIG. 15  shows a top view of a second exemplary workstation arrangement using dual quad-track beam assemblies. 
         FIG. 16  shows a perspective view of an exemplary embodiment of a single-track beam assembly. 
         FIG. 17  shows a perspective view of an exemplary embodiment of a dual-track beam assembly. 
         FIG. 18  shows a perspective view of a third exemplary workstation arrangement. 
         FIG. 19A  shows a side view of the third exemplary workstation arrangement with a cable trough and a shelf coupled thereto. 
         FIG. 19B  shows a perspective view of the cable trough of  FIG. 19A . 
         FIG. 20  shows a perspective view of an adjustable end bracket. 
         FIG. 21  shows a top view of a fourth exemplary workstation arrangement. 
         FIG. 22  shows a top view of a fifth exemplary workstation arrangement. 
         FIG. 23  shows a top view of a sixth exemplary workstation arrangement, demonstrating some of the different shaped work surfaces that may be used to create customized workstations for multiple purposes. 
     
    
    
     DETAILED DESCRIPTION 
     Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy. 
     In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
     Use of directional terms such as “upper,” “lower,” “above,” “below”, “in front of,” “behind,” etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference. 
     Those skilled in the art will recognize that numerous modifications and changes may be made to the exemplary embodiment(s) without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the exemplary embodiment(s) is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof. 
     QUAD-TRACK BEAM—FIRST EXEMPLARY EMBODIMENT 
       FIG. 1  is a perspective view of a first embodiment of a quad-track beam  100 . Typically, the quad-track beam  100  would have an end cap, but this is omitted in  FIG. 1  to better illustrate the cross-sectional structure of the first embodiment quad-track beam  100 . The first embodiment quad-track beam  100  has four corner tubes  104 . The corner tubes  104  are much greater in length than in width, typically 20 or more inches in length and one to two inches in width. The corner tubes  104  are arranged in parallel longitudinally and in a rectangular pattern in cross-section. The corner tubes  104  in the first embodiment quad-track beam  100  are made of steel in 12, 14, or 16 gauges, however in other embodiments, other suitable materials may be used. The corner tubes  104  have interior sides  106  that face inward towards the other corner tubes  104  and have exterior sides  107  facing outward. 
     The first embodiment quad-track beam  100  also has four channel bars  108 . Each of the first embodiment channel bars  108  has two lateral sides  110  and a back side  112 . Collectively, the lateral sides  110  and the back side  112  define a channel bar cavity  114  therein. Each corner tube  104  is coupled to two of the other corner tubes  104  by one of the channel bars  108  with each lateral side  110  of each of the channel bars  108  contacting one of the interior sides  106  of one of the corner tubes  104 . In the first embodiment, the channel bars  108  are made of steel and welded to the corner tubes  104 , but in other embodiments, may be made of other materials and attached in other ways. 
       FIG. 2  shows a detailed view of one of the channel bars  108  along with a strut-nut  140 . The strut-nut  140  is used to attach an accessory (e.g., the single channel leg  120  in  FIG. 1 ) to the first embodiment quad-track beam  100  at the channel bar  108 . Each of the channel bars  108  has channel bar lips  116  that curl in towards each other and then towards the channel bar cavity  114  and the back side  112  of the channel bar  108 . The channel bar cavity  114  has nut-retention foam  118  placed therein. The channel bar  108  is configured to hold the strut-nut  140  against the curled channel bar lips  116  with the nut-retention foam  118 . The channel bar  108  has a space between the channel bar lips  116  that is slightly larger than the width of the strut-nut  140 . The strut-nut  140  can be inserted into the channel bar cavity  114 , pushing back the nut-retention foam  118 . Then the strut-nut  140  can be twisted so that the ends of the longer dimension of the strut-nut  140  slip under the channel bar lips  116 . The strut-nut  140  has a pair of toothed grooves  148  near the ends of its longer dimension that are configured to engage with the channel bar lips  116 . The strut-nut  140  has two rounded corners  142 , diagonally opposed and two angled corners  144 , diagonally opposed. The longer dimension of the strut-nut  140  is configured to be slightly shorter than the interior width of the channel bar cavity  114 . When the strut-nut  140  is twisted clockwise, the rounded corners  142  slide past the interior lateral walls of the channel bar  108  until the angled corners  144  contact the channel bar lateral side  110 , preventing further clockwise rotation of the strut-nut  140 . The strut-nut  140  also has a threaded hole  146  configured to accept a threaded rod, bolt or screw, which is used to attach an accessory (such as the single channel leg  120 ) to the first embodiment quad-track beam  100 . 
     In the first embodiment, the corner tubes  104  are square in cross-section, but in other embodiments may be rectangular. A rectangular cross-section provides flat corner tube interior sides  106  for joining with the flat lateral sides  110  of the channel bars  108 . The rectangular cross-section provides a flat surface for accommodating accessory parts (e.g., the single channel leg  120  in  FIG. 1 ). This allows the accessory parts to have large flat end plates (e.g. the single channel leg end plate  128  in  FIG. 1 ) for contacting the corner tubes  104 . Large flat end plates facilitate transmittal of torque from the accessory to the first embodiment quad-track beam  100 . Such torque would occur if the accessory is cantilevered off of the quad-track beam  100 . Any torque placed on the accessory will transmit the torque forces mostly through the leg end plate  128  to the corner tubes  104  and not as much through the hardware (i.e., the bolt, strut-nut  140 , and channel bar lips  116 ) attaching the accessory to the quad-track beam  100 . Torsion transmitted solely through the strut-nut  140  would tend to unseat the strut-nut  140  from one of the channel bar lips  116  and double the stress on the other channel bar lip  116 . This would reduce the torque that could be safely handled by the quad-track beam  100  and accessory combination. 
     In the first embodiment, the channel bar lips  116  are flush or nearly flush with the exterior sides  107  of the corner tubes  104 . This is to facilitate the coupling of accessories, which is more difficult when the channel bar  108  is recessed. The channel bar lateral sides  110  are just long enough to provide sufficient depth in the channel bar cavity  114  for insertion of a strut-nut  140 . This keeps the channel bar back side  112  close to the exterior of the quad-track beam  100 , as defined by the exterior sides  107  of the adjacent corner tubes  104 . The channel bar back sides  112  bear forces caused by torsion of the quad-track beam  100  about its long axis and will do so more efficiently when they are closer to the exterior of the quad-track beam  100 . In the first embodiment, the channel bar lateral sides  110  in cross-section are no greater in length than the corner tube interior sides  106  with which they are in contact. More specifically, the channel bar lateral sides  110  in cross-section are half or less in length than the corner tube interior sides  106  with which they are in contact. In the first embodiment, the corner tubes  104  are square in cross-section with corner tube interior sides  106  of 1½ inches and the channel bar lateral sides  110  are ¾ inches. 
     QUAD-TRACK BEAM—SECOND EXEMPLARY EMBODIMENT 
       FIG. 3  shows a second embodiment of a quad-track beam  156  and a jam nut  168  intended for use therewith. Similar to the first embodiment quad-track beam  100 , the second embodiment quad-track beam  156  has four corner tubes  158  that are rectangular in cross-section and arranged in a rectangular pattern in cross-section. The corner tubes  158  have interior sides  161  that face inward towards the other corner tubes  158  and have exterior sides  159  facing outward. However, instead of channel bars, these four corner tubes  158  are coupled by side plates  162 . In the second embodiment, each side plate  162  is coupled to an adjacent two of the corner tubes  158  to be flush with the exterior sides  159  of the adjacent two corner tubes  158 . In other embodiments, the adjacent corner tubes  158  are nearly flush with the exterior sides  159  of the two adjacent corner tubes  158 , with each of the side plates  162  in cross-section no farther from one of the exterior sides  159  than a half of a length in cross-section of an adjacent one of the interior sides  161 . The side plates  162  bear the torsion forces generated when a torque is applied to the quad-track beam  156  about its long axis. In the second embodiment, the side plates  162  are coupled to the corner tubes  158  by welding, but in other embodiments, may be coupled in other ways. In some embodiments, the second embodiment quad-track beam  156  is extruded as a monolithic piece. 
     The corner tubes  158  in the second embodiment quad-track beam  156  are made of steel in 12, 14, or 16 gauges. The side plates  162  are made of 14 gauge steel. However in other embodiments, other suitable materials may be used for the corner tubes  158  and side plates  162 . In a cross-section of the second embodiment quad-track beam  156 , the corner tubes  158  are 1½ inches on each side and the side plates  162  are 1½ inches wide. However, in other embodiments, the corner tubes  158  and side plates  162  may have other dimensions. 
     The side plates  162  of the second embodiment quad-track beam  156  have slots  164  for insertion of the jam nut  168 . The side slots  164  run along the long axis of the side plate  162 , interrupted by side plate webs  166 . The side plate webs  166  bear the forces caused by torsion of the second embodiment quad-track beam  156  about its long axis. The side slots  164  have a width parallel to the long axis of the side plate  162  and a height orthogonal to the width. The width of each of the side slots  164  is at least as wide as the length (largest dimension) of the jam nut  168 . The height of each of the side slots  164  is at least as high as the thickness (smallest dimension) of the jam nut  168 . In the second embodiment, the side slots  164  are 9/16 inch high, which is slightly larger than the ⅜ inch thickness of the jam nut  168  used to attach accessories. In other embodiments, the side slots  164  may have a different height. For example, in some embodiments, the height of the side slots  164  is at least as high as the width of the jam nut  168  intended to be used. This would allow the jam nut  168  to be inserted into one of the side slots  164  while a bolt or threaded rod is inserted into a threaded hole  174  of the jam nut  168 . 
     Longer side slots  164  and shorter side plate webs  166  will weaken resistance of the second embodiment quad-track beam  156  to torsion about its long axis, and shorter side slot  164  with longer side plate webs  166  will strengthen resistance to torsion. A trade-off must be made between the better torsion resistance of shorter side slots  164  and flexibility in attaching accessories that comes from longer side slots  164 . In the second embodiment, the side slots  164  are 4 inches wide and the side plate webs  166  are 1 inch wide, but other embodiments may have different widths for these features. 
     The second embodiment quad-track beam  156  has a central cavity  176  defined by the corner tubes  158  and the side plates  162 . The central cavity  176  has a nut-retention foam  160  positioned therein. The nut-retention foam  160  is compressible and resilient. A jam nut  168  to be inserted through one of the side slots  164  compresses the nut-retention foam  160 . The resilience of the nut-retention foam  160  then holds the jam nut  168  in position. 
     Similar to the strut-nut  140  in the first embodiment, the purpose of the jam nut  168  is to attach accessories to the second embodiment quad-track beam  156 . The jam nut  168  can be inserted into the central cavity  176 , pushing back the nut-retention foam  160 . Then the jam nut  168  can be twisted so that the ends of the longer dimension of the jam nut  168  slip behind the side plate  162 . The jam nut  168  has two rounded corners  170 , diagonally opposed and two angled corners  172 , diagonally opposed. The longer dimension of the jam nut  168  is configured to be slightly shorter than the width of the side plate  162 , where the width refers to the dimension between the corner tubes  158 . When the jam nut  168  is twisted clockwise, the jam nut rounded corners  170  slide past the corner tubes  158  until the angled corners  172  contact the corner tubes  158 , preventing further clockwise rotation of the jam nut  168 . The jam nut  168  also has a threaded hole  174  configured to accept a threaded rod, bolt or screw, which is used to attach an accessory to the second embodiment quad-track beam  156 . 
     QUAD-TRACK BEAM—THIRD EXEMPLARY EMBODIMENT 
       FIG. 8  shows a third embodiment of a quad-track beam  230 . Similar to the first embodiment quad-track beam  100 , the third embodiment quad-track beam  230  has four corner tubes  232  arranged in a rectangular pattern in cross-section. However, instead of channel bars, these four corner tubes  232  are coupled by four corner tube webs  238 . The four corner tube webs  238  define a central cavity  240 . The third embodiment quad-track beam  230  is more suitable for manufacturing by extrusion than the first or second embodiments, but all three embodiments may be made by various manufacturing methods without limitation. 
     The corner tubes  232  each have a corner tube cavity  234 . The corner tubes  232  are each generally rectangular in shape in cross-section with some rounded corners, but in other embodiments may have circular cross-sections or some other suitable shape. The corner tubes  232  each have at least one exterior side  248  and at least one interior side  246 . The corner tubes  232  each have two corner tube lips  236  that each project from one of the interior sides  246  of the corner tube  232  towards an adjacent corner tube  232 . Each two corner tubes  232 , the corner tube web  238  between them and the corner tube lips  236  adjacent this corner tube web  238 , together define a channel cavity  242 . 
     The channel cavity  242  is “T” shaped to accept a jam nut, similar to the jam nut  168  of the second embodiment. The jam nut is configured to be inserted into the channel cavity  242  with its length axis parallel to the length of the channel cavity  242 , and then turned so that its length axis is parallel to the width of the channel cavity  242 . With a jam nut that has a length that is the same dimension as the width of the channel cavity  242 , the jam nut will jam against the corner tubes  232 . The jam nut can be used to attach an accessory much in the same way as the strut-nut  140  of the first embodiment or the jam nut  168  of the second embodiment. 
     Each of the four corner tubes  232  has a corner tube neck  244  projecting from the corner tube  232  towards the center of the rectangular pattern of corner tubes  232 . Each corner tube neck  244  connects that corner tube  232  with the two closest corner tube webs  238 . Each corner tube neck  244  is relatively thick to facilitate transmittal of torsion force from an adjacent corner tube  232  to the adjacent corner tube webs  238  without undue bending or deformation of the corner tube neck  244 . If the corner tube neck  244  is too thin, an accessory cantilevered off of the third embodiment quad-track beam  230  and attached with a jam nut in one of the channel cavities  242  would bend the corner tube  232  above the channel cavity  242  back and away from the channel cavity  242 , potentially unseating and releasing the jam nut. To prevent this, each of corner tube necks  244  is at least as thick as half the distance between the adjacent corner tube cavity  234  and the central cavity  240 . 
     To facilitate transmittal of torque about the long axis of the third embodiment quad-track beam  230  without undue twisting, the corner tube webs  238  are relatively thick and as close to the outer edge of the third embodiment quad-track beam  230  as possible. Each corner tube web  238  is at least as thick as half one of the adjacent corner tube necks  244 . Each corner tube web  238  is at least closer to the outer edges of the third embodiment quad-track beam  230  than to a center of the central cavity  240 . Stated differently, each corner tube web  238  is at least closer to one of the exterior sides  248  one of the corner tubes  232  than to a center of the central cavity  240 . 
     BASIC ASSEMBLIES AND ACCESSORIES USING QUAD-TRACK BEAMS 
       FIGS. 4 a -4 d    show four basic configurations that can be made with a quad-track beam. The first embodiment quad-track beam  100  is used in  FIGS. 4 a -4 d   , but second embodiment quad-track beam  156  may be used or any other embodiment of quad-track beam consistent with the teachings herein.  FIG. 4 a    shows a straight configuration  200 , which is just a single quad-track beam.  FIG. 4 b    shows a diamond configuration  202 , in which the mitered ends of 4 quad-track beams are joined.  FIG. 4 c    shows a cross configuration  204 , in which the ends of 4 quad-track beams are joined at a central junction point.  FIG. 4 d    shows a star configuration  206 , in which is like the diamond configuration  202  except that it has 4 additional side beams, one in each junction between the mitered ends of the quad-track beams in the diamond. 
       FIG. 5 a    shows a star joint  208  in the star configuration  206 . Three first embodiment quad-track beams  100  are joined by a star joint plate  210 . The star joint plate  210  is joined to the channel bar cavities  114  of the quad-track beams  100  with threaded bolts  212 .  FIG. 5 b    shows a diamond joint  214  in the diamond configuration  202 . Two first embodiment quad-track beams  100  are joined by a diamond joint plate  216 . The diamond joint plate  216  is joined to the channel bar cavities  114  of the quad-track beams  100  with threaded bolts  212 . 
     One type of accessory that can be joined to a quad-track beam is a channel leg.  FIGS. 6 a -6 d    show several embodiments of channel legs.  FIG. 6 a    is a perspective view of a single channel leg  120  and  FIG. 6 b    is a cross-section view of a single channel leg  120  from the top. The single channel leg  120  has a leg body  126  and a leg end plate  128 . The leg body  126  comprises a “C” type channel. The leg end plate  128  is joined to one end of the leg body  126  and has one or more bolt holes  129 . The bolt holes  129  allow the single channel leg  120  to be attached to a quad-track beam with a threaded bolt and a nut that jams in the quad-track beam, such as a strut-nut  140  or jam nut  168 . The single channel leg  120  has a leg cavity  122 . In some embodiments, such as the embodiment shown in  FIG. 6 b   , the single channel leg  120  has nut-retention foam  124  positioned therein, which makes it possible to attach other accessories to the single channel leg  120  in the same manner as they are attached to the quad-track beam. However, the single channel leg  120  is not as resistant to torsion about its long axis as is a quad-track beam, so it will not be able to cantilever as much load as a quad-track of similar size. In other embodiments, such as the embodiment shown  FIG. 6 a   , the single channel leg  120  does not have any nut-retention foam. 
       FIG. 6 c    is a cross-section view of an alternative single channel leg  130 . The alternative single channel leg  130  has a leg channel  132  bracketed by two leg tubes  134 . The leg channel  132  has nut-retention foam  136  positioned therein, but may be omitted in some embodiments. The alternative single channel leg  130  has an end plate (not shown) similar to the leg end plate  128  in  FIG. 6   a.    
       FIG. 6 d    is a cross-section view of a double channel leg  180 . The double channel leg  180  has a front channel  182  and a back channel  184  that are joined back-to-back. The double channel leg  180  has an end plate (not shown) similar to the leg end plate  128  in  FIG. 6 a   . The double channel leg  180  has nut-retention foam  186  positioned therein, but may be omitted in some embodiments. 
     WORKSTATION ASSEMBLIES USING QUAD-TRACK BEAMS 
       FIG. 7  shows a first application using quad-track beams. First embodiment quad-track beams  100  are used, but second embodiment quad-track beams  156  or other embodiments of the quad-track beam could be used. A first embodiment quad-track beam  100  is supported by two single channel legs  120  attached thereto. A first side extension  220  and a second side extension  222  are attached to the quad-track beam  100  using gusset plates  224 , threaded bolts  212  and strut-nuts  140 . The first side extension  220  has a single channel leg  120  to support its far end, but the second side extension  222  does not and is cantilevered. Due to the attachment mechanism described herein, the side extensions can be moved laterally after loosening the appropriate threaded bolts  212 . When in the desired position, the threaded bolts  212  are tightened. Other accessories can be attached to the side extensions  220 ,  222  such as shelves, bins, computer pedestals and table top work surfaces. A divider  226  is attached to the first embodiment quad-track beam  100  using a gusset plate  224 , threaded bolts  212  and strut-nuts  140 . The divider  226  is shown as cantilevered from the first embodiment quad-track beam  100 , but it could also be supported at the far end by a single channel leg  120 . 
     QUAD-TRACK BEAM—FOURTH EXEMPLARY EMBODIMENT 
       FIGS. 9A and 9B  show a fourth embodiment of a quad-track beam  230 .  FIG. 9A  shows the fourth embodiment quad-track beam  260  in a perspective view.  FIG. 9B  shows an exploded perspective view of the fourth embodiment quad-track beam  260 . The fourth embodiment quad-track beam  260  has four angle bars  264  arranged in parallel lengthwise. The angle bars  264  are arranged in a pattern  270  that is rectangular in cross-section. The rectangular cross-section pattern  270  has four pattern corners  272 . Each of the four angle bars  264  have two legs  266  that join at an angle bar corner edge  268 . The angle bar corner edge  268  of each of the four angle bars  264  is located in a different one of the four pattern corners  272 . The four angle bars  264  are arranged such that there is an inter-bar gap  276  between each leg  266  and an adjacent leg  266  of an adjacent angle bar  264 . The inter-bar gap  276  may serve as a track for attaching accessories or attaching the quad-track beam  260  to other copies of the quad-track beam  260  or to other structures. 
     The angle bars  264  in the fourth embodiment quad-track beam  260  are made of steel 3/16 inch thick, however in other embodiments, other suitable materials and thicknesses may be used. The angle bars  264  may be a length suitable for constructing workstations. A length of 60 inches is usually suitable, but other lengths may prove to be desirable. The angle bar legs  266  may have a suitable width, such as 1½ inches, but may have other widths. The inter-bar gap  276  may have a suitable width, such as ¾ inches, but may have other widths as well. Length and thickness of the angle bars  264  may be selected based on the situations in which the quad-track beam  260  is intended to be used. Situations that will put more torsion on the quad-track beam  260  may call for thicker angle iron. 
     In the fourth embodiment quad-track beam  260 , the four angle bars  264  are coupled with one or more beam mount brackets  274 . Typically, there is one beam mount bracket  274  every 30 inches down the length of the quad-track beam  260 , but other spacing may be used. The beam mount bracket  274  is formed in a shape of a rectangular tube. Each of the four corners of the beam mount bracket  274  is nested inside of one of the four angle bars  264  and coupled thereto. The beam mount bracket  274  may be coupled to the four angle bars  264  by welding, by threaded bolts and nuts or some other suitable coupling. In  FIG. 9A , the beam mount bracket  274  is shown as coupled to the four angle bars  264  by welding. In  FIG. 9B , the beam mount bracket  274  and the four angle bars  264  have bolt holes for facilitating coupling with threaded bolts (not shown). 
       FIG. 9C  shows the fourth embodiment quad-track beam  260  in a perspective view with components for attaching accessories. The fourth embodiment quad-track beam  260  has a central cavity  176  defined by the four angle bars  264 . A block of nut-retention foam  186  is positioned within the cavity. Attachment of accessories to the fourth embodiment quad-track beam  260  is accomplished in a manner very similar to the second embodiment quad-track beam  156 . A jam nut  168  may be inserted into one of the inter-bar gaps  276  and twisted into an orientation perpendicular to the inter-bar gap  276 . A bolt or threaded rod may be inserted into a threaded hole  174  of the jam nut  168  and the bolt be tightened, compressing the accessory and the jam nut  168  against the angle bars  264 . A bolt plate  280  with two jam nut hole  174  may be inserted into one of the inter-bar gaps  276  in a similar manner, but without twisting. Both the jam nut  168  and the bolt plate  280  provide an extent of surface engagement with the angle bars  264  to provide a high amount of resistance to torqueing or lateral movement. 
     DUAL QUAD-TRACK BEAM ASSEMBLY—FIRST EXEMPLARY EMBODIMENT 
       FIG. 10A  shows a top view of a first embodiment of a dual quad-track beam assembly  262 . The dual quad-track beam assembly  262  provides a stronger base from which to build a work station than just a single quad-track beam and also provides a second row of inter-bar gaps  276  on the same face, which can be convenient for building work stations on both sides of the dual quad-track beam assembly  262 . The dual quad-track beam assembly  262  comprises two of the fourth embodiment quad-track beams  260  coupled together with a plurality of dual beam brace brackets  282 .  FIG. 10B  shows a perspective view of a dual beam brace bracket  282 . The dual beam brace brackets  282  are coupled to the quad-track beams  260  by welding, bolting or some other suitable coupling. The dual beam brace bracket  282  has bolt holes  278  in its legs for coupling with a quad-track beam  260  and has bolt holes  278  in its back plate for coupling with other dual quad-track beam assemblies  262  or coupling with mounting brackets for accessories. 
     Bolting of the dual quad-track beam assembly  262  and of the constituent quad-track beams  260  provides a logistical advantage as separate angle bars  264 , beam mount brackets  274 , and dual beam brace brackets  282  can be stored, shipped and moved more conveniently than fully assembled dual quad-track beam assemblies  262 . The dual quad-track beam assembly  262  may be made to any convenient length. A typical configuration would be a dual quad-track beam assembly  262  of 120 inches with dual beam brace brackets  282  at each end and at 30 inch intervals. 
     DUAL QUAD-TRACK BEAM ASSEMBLY—SECOND EXEMPLARY EMBODIMENT 
       FIGS. 11A and 11B  show views of a second embodiment of a dual quad-track beam assembly  284 .  FIG. 11A  shows a perspective view of the second embodiment of a dual quad-track beam assembly  284 .  FIG. 11B  shows a top view of the second embodiment of a dual quad-track beam assembly  284 . The second embodiment dual quad-track beam assembly  284  comprises two quad track beams made of two sets of four angle bars  264 , each arranged as in the fourth embodiment quad-track beam  260  as shown in  FIG. 9A , but without the beam mount brackets  274 . Instead, the four angle bars  264  are coupled together by quad-track end plates  286 , one at each end. The quad-track end plates  286  are preferably coupled to the four angle bars  264  by welding, but bolting or some other suitable coupling may be used. 
     As shown in  FIG. 11A , a single quad-track end plate  286  not only couples angle bars  264  of one of the quad-track beams, but both. The quad-track end plates  286  have bolt holes  278  to allow one dual quad-track beam assembly  284  to be coupled to another such assembly and alternatively to allow accessories to be attached. The second embodiment dual quad-track beam assembly  284  has a plurality of stiffeners  288  coupled to the angle bars  264  in the inter-bar gaps  276 , preferably by welding. The stiffeners  288  reinforce the quad-track beam, transmitting compression force and helping maintain the size and integrity of the inter-bar gap  276  when the quad-track beam is under torsion about its long axis. 
     DUAL QUAD-TRACK BEAM CRUCIFORM MODULE—FIRST EXEMPLARY EMBODIMENT 
       FIG. 12  shows a perspective view of a first embodiment of a dual quad-track beam cruciform module  292 . The first embodiment dual quad-track beam cruciform module  292  comprises a plurality of dual quad-track beam assemblies coupled in a cruciform shape. The dual quad-track beams assemblies used in the first embodiment dual quad-track beam cruciform module  292  may be either of the first embodiment dual quad-track beam assembly  262  type or of the second embodiment dual quad-track beam assembly  284  type. The plurality of dual quad-track beam assemblies comprises one long dual quad-track beam assembly  298  and two short dual quad-track beam assemblies  300 . The two short dual quad-track beam assemblies  300  are coupled to the long dual quad-track beam  298  using sets of bolts and jam nuts, such as the jam nut  168  shown in  FIG. 9C . Each set of bolts and jam nuts are inserted into one of the inter-bar gaps  276  in the long dual quad-track beam  298 . 
     DUAL QUAD-TRACK BEAM CRUCIFORM MODULE—SECOND EXEMPLARY EMBODIMENT 
       FIG. 13A  shows a perspective view of a second embodiment of a dual quad-track beam cruciform module  294 . The second embodiment dual quad-track beam cruciform module  294  has four dual quad-track beam assemblies, each coupled to a central mounting plate  296 . The dual quad-track beams assemblies used in the first embodiment dual quad-track beam cruciform module  292  may be either of the first embodiment dual quad-track beam assembly  262  type or of the second embodiment dual quad-track beam assembly  284  type.  FIG. 13B  shows a perspective view of the central mounting plate  296 . 
     SINGLE-TRACK BEAM ASSEMBLY—EXEMPLARY EMBODIMENT 
       FIG. 16  shows a perspective view of an exemplary embodiment of a single-track beam assembly  316 . The single-track beam assembly  316  comprises two single-track beams coupled in parallel lengthwise with an inter-beam gap  320  between them. Each of the two single track beams comprises two angle bars  264  coupled in parallel lengthwise and in a pattern that is rectangular in cross-section. The two angle bars  264  are arranged such the corner edge of each of the two angle bars  264  is in a different one of the four pattern corners and such that there is an inter-bar gap  276  between one of the legs  266  of two angle bars  264  and an adjacent one of the legs  266  of a second of the two angle bars  264 . The single-track beam assembly  316  has two end plates  318 , each coupled to one of the ends of the angle bars  264  of both single-track beams. The single-track end plates  318  are preferably coupled to the angle bars  264  by welding, but other couplings may be used. 
     The single-track beam assembly  316  may be used to provide support for mounting additional accessories to a work station. The single-track beam assembly  316  is not as strong in resisting torsion along its long axis as the quad-track beams, but in situations where no such torsion loads are expected, the single-track beam assembly  316  is a lighter weight alternative. Such situations would include where accessories are only mounted vertically and not cantilevered out sideways. 
     DUAL-TRACK BEAM ASSEMBLY—EXEMPLARY EMBODIMENT 
       FIG. 17  shows a perspective view of an exemplary embodiment of a dual-track beam assembly  322 . The dual-track beam assembly  322  has two dual-track beams coupled in parallel lengthwise with an inter-beam gap  320  between them. Each of the two dual track beams comprises two channel bars  326  coupled in parallel lengthwise and in a pattern that is rectangular in cross-section. Each of the two channel bars has two channel bar legs  328  joined to a channel back  330 . The channel back  330  of one of the two channel bars  326  is in two of the four corners of the rectangular pattern and the channel back  330  of other of the two channel bars  326  is in the other two of the four corners of the rectangular pattern. The two channel bars  326  are arranged such that for each channel bar leg  328  there is an inter-bar gap  276  between that leg and an adjacent one of the legs of the other of the two channel bars  326 . The dual-track beam assembly  322  has two dual-track end plates  324  coupled to the ends of the channel bars  326  of both dual-track beams. The dual-track end plate  324  are preferably coupled to the channel bars  326  by welding, but other couplings may be used. 
     The dual-track beam assembly  322  may be used to provide support for mounting additional accessories to a work station. The dual-track beam assembly  322  is stronger than the single-track beam assembly  316 , but not as strong as the quad-beam assemblies in resisting torsion along its long axis. However, in situations where no such torsion loads are expected, the dual-track beam assembly  322  is an intermediate weight alternative. 
     DUAL QUAD-TRACK BEAM ASSEMBLY—APPLICATION EXAMPLES 
       FIG. 14A  shows a perspective view of a dual quad-track beam assembly with cantilevered legs  304  attached, forming a first exemplary workstation arrangement  308 . Second embodiment dual quad-track beam assemblies  284  are shown, but first embodiment dual quad-track beam assembly  262  may be used as well. The cantilevered legs  304  couple to the dual quad-track beam assembly  284 , elevating the second embodiment dual quad-track beam assembly  284  to a useful height for when work surfaces and work accessories are attached thereto. The cantilevered legs  304  each have a leg mounting plate  306  with bolt holes  278  therein.  FIG. 14B  shows a top view of the leg mounting plate  306 . The leg mounting plate  306  is coupled to the second embodiment dual quad-track beam assembly  284  using sets of bolts and jam nuts, such as the jam nut  168  shown in  FIG. 9C . Each set of bolts and jam nuts are inserted into one of the inter-bar gaps  276  in the underside of dual quad-track beam assembly  284 . Any of the cantilevered legs  304  can be repositioned along the dual quad-track beam assembly  284  by loosening of the bolts in the leg mounting plate  306 , then sliding the cantilevered leg  304  forward or back along the dual quad-track beam assembly  284  as indicated by the arrows. 
       FIG. 15  shows a top view of a second exemplary workstation arrangement  310  using dual quad-track beam assemblies  284 . Second embodiment dual quad-track beam assemblies  284  are shown, but first embodiment dual quad-track beam assembly  262  may be used as well. An accessory  312  may be coupled to one of the dual quad-track beam assemblies  284  anywhere there is inter-bar gap  276  available to do so. The accessory  312  is coupled to an accessory mounting  314 . The accessory mounting  314  has bolt holes  278  therein. The accessory mounting  314  couples to the dual quad-track beam assembly  284  using sets of bolts and jam nuts, such as the jam nut  168  shown in  FIG. 9C . Each set of bolts and jam nuts are inserted into one of the inter-bar gaps  276  in the topside of dual quad-track beam assembly  284 . 
       FIG. 18  shows a perspective view of a third exemplary workstation arrangement  332 . This third exemplary workstation arrangement  332  has one or more second embodiment dual quad-track beam assemblies  284  with cantilevered legs  304  attached as in the first exemplary workstation arrangement  308  as shown in  FIG. 14A , but also has one or more adjustable accessory brackets  334  and a work surface  336  (shown as transparent to allow view of the adjustable accessory brackets  334 ). 
     The adjustable accessory brackets  334  each have a bracket tube  338  and a bracket mounting plate  340 . The bracket mounting plate  340  couples to the dual quad-track beam assembly  284  using sets of bolts and jam nuts, such as the jam nut  168  shown in  FIG. 9C . The bracket tube  338  is coupled to the bracket mounting plate  340 . A bracket arm  342  is inserted into and slidingly coupled with the bracket tube  338 . Accessories may be mounted to the bracket arm  342 , such as the work surface  336  shown. The bracket arm  342  may be moved within the bracket tube  338  to adjust the height of the accessory. Alternatively, the adjustable accessory bracket  334  may be mounted with the bracket tube  338  pointing sideways rather than vertically, in which case, the lateral position of the accessory is adjusted. The bracket arm  342  may be held in position with a set screw  344 , which may be loosened to reposition the bracket arm  342  and tightened again when in the new position. The set screw  344  may have a hand knob so that the position of the bracket arm  342  can be adjusted without tools. 
     Bracket arm  342  shown in  FIG. 18  has a right angle bend for supporting the work surface  336 , but other bracket arms  342  may not have the right angle bend and may have different ways for connecting with accessories, such as pivot joints. 
       FIG. 19A  shows a side view of the third exemplary workstation arrangement  332  with a cable trough  346  and a shelf  348  coupled thereto. The shelf  348  may be coupled to the dual quad-track beam assembly  284  using sets of bolts and jam nuts. The shelf  348  may be used to hold tools, light fixtures, boxes of parts, etc.  FIG. 19B  shows a perspective view of the cable trough  346  with a curled lip  350  on either side. The curled lips  350  may clip into the inter-bar gap  276  of the quad-track beams  260  of the dual quad-track beam assembly  284  and engage with the upper edge of one of the angle bar legs  266  (see  FIG. 9C ). The cable trough  346  may be used to carry power and communications cables to various workstations. 
       FIG. 20  shows a perspective view of an adjustable end bracket  352 . The adjustable end bracket  352  has an end bracket back  354  with two bracket tubes  338  attached thereto and two bracket arms  342  positioned within and slidingly coupled to the bracket tubes  338 . Each of the two bracket arms  342  may be held in position with a set screw  344 , which may be loosened to reposition the bracket arm  342  and tightened again when in the new position. The end bracket back  354  has one or more bolt holes  278  matching the bolt holes  278  in a quad-track end plate  286  in a second embodiment dual quad-track beam assembly  284  or dual beam brace bracket  282  in a first embodiment dual quad-track beam assembly  262 , which allows the adjustable end bracket  352  to be coupled to one end of a first embodiment dual quad-track beam assembly  262  or a second embodiment dual quad-track beam assembly  284 . 
       FIG. 21  shows a top view of a fourth exemplary workstation arrangement  356 . The fourth exemplary workstation arrangement  356  comprises a first embodiment dual quad-track beam cruciform module  292 , although a second embodiment dual quad-track beam cruciform module  294  could be used as well. The dual quad-track beam cruciform module  292  has cantilevered leg  304  coupled to its underside (hidden in this drawing). An end zone work surface  358  is coupled to the end of each of the four arms of the dual quad-track beam cruciform module  292  with a bracket arm  342  held by an adjustable end bracket  352 . Work surface support frame  360  may be coupled to the adjustable bracket arm  342  to help support the end zone work surface  358 . One worker can stand in each space between the end zone work surfaces  358  with the end zone work surface  358  used as collaborative work areas. In  FIG. 21 , all four end zone work surfaces  358  are shown as having the same shape, but in other arrangements, each of the end zone work surfaces  358  may have a different shape. 
       FIG. 22  shows a top view of a fifth exemplary workstation arrangement  362 . The fifth exemplary workstation arrangement  362  comprises a first embodiment dual quad-track beam cruciform module  292 , although a second embodiment dual quad-track beam cruciform module  294  could be used as well. The dual quad-track beam cruciform module  292  has cantilevered legs  304  coupled to its underside (hidden in this drawing). Several work surfaces  364  mounted on work surface support frames  360  are coupled to the dual quad-track beam cruciform module  292  with adjustable accessory brackets  334 . Each of the work surface support frames  360  has bracket arms  342  that sliding couple with the respective adjustable accessory brackets  334 , allowing for adjustment of the height of the work surfaces  364 . Several of the bracket arms  342  have pivots  366  coupling the bracket arm  342  to the respective work surface support frame  360  and work surface  364 , allowing that work surface  364  to be tilted to various angles. 
       FIG. 23  shows a top view of a sixth exemplary workstation arrangement  368 , demonstrating some of the different shaped work surfaces that may be used to create customized workstations for multiple purposes. The sixth exemplary workstation arrangement  368  comprises two first embodiment dual quad-track beam cruciform modules  292 , although second embodiment dual quad-track beam cruciform module  294  could be used as well or a combination thereof. The dual quad-track beam cruciform modules  292  have cantilevered legs  304  coupled to its underside (hidden in this drawing). Different shaped work surfaces are attached to the dual quad-track beam cruciform modules  292 , including a work surface with circular cutout  370 , a work surface with semi-circular cutout  372 , a work surface with small wing  374 , a work surface with large wings  376 , a work surface with triangular cutout  378 , and an intermediate work surface  380 . The intermediate work surface  380  couples to one of the ends of each of the two dual quad-track beam cruciform modules  292 , joining them together in a single unit.

Summary:
Embodiments of a multi-track beam for use in modular assembly systems for office and industrial work stations. The embodiments have four corner tubes, bars, or channels arranged in a rectangular pattern in cross-section and connected in ways that provide improved ability to transmit torque along a long axis of the multi-track beam while providing improved resistance to bending under the forces of the torque. Fastening devices such a jam nuts may be inserted into the tracks to secure accessories to the multi-track beam or to other multi-track beams.