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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
   The invention relates to suspended ceiling systems and, in particular, to a novel clip for suspending a pair of main tees in parallel relation. 
   PRIOR ART 
   Certain ceiling treatments or designs utilize main tees in relatively closely spaced pairs to give a ceiling a distinctive appearance and/or to provide an intermediate space for lighting, HVAC systems, sprinkler systems and like services. It is known to use a series of special clips to support a pair of main tees in parallel relation. Such clips, typically, are suspended directly from overhead structure by steel wire. In certain geographic areas, local codes or requirements prohibit suspended ceilings from being suspended from overhead structure directly by plain wire ties. For example, in some areas, a C-channel must first be hung from the overhead structure and a suspended ceiling, fixtures and-like elements must be hung from these intermediate channels. As far as is known, there are no available clips or brackets that can be easily and quickly attached to the suspension channels that, in turn, can support a pair of main tees in a uniform parallel spacing. 
   SUMMARY OF THE INVENTION 
   The invention provides a clip that is compatible with overhead channel suspension and which supports a pair of grid main tees in precise parallel alignment. The clip of the invention is easy to use and thereby saves installation time and avoids fatigue on the part of the installer. 
   In its preferred form, the clip is arranged to work with prior art “drop clip” hangers compatible with the required overhead suspension channels. As disclosed, the clip is coupled to a hanger with simple manipulation of the hanger and clip elements without the need for the use of tools and/or separate fasteners. The compatibility of the disclosed clip with conventional drop clip C-channel hangers significantly reduces the cost and complexity of the tooling required to make the clip and, therefore, reduces the costs involved in making the clip. Additionally, the clip affords the known benefits of similar clips in producing a uniform spacing between the grid tee pairs which spacing is critical since variations are conspicuous to even the casual observer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective fragmentary view of a pair of parallel grid tees supported by the clip of the invention from an overlying suspended structural channel; 
       FIG. 2  is a cross-sectional view of the spaced parallel grid tees and clip taken in the plane  2 - 2  indicated in  FIG. 1 ; 
       FIG. 3  is an elevational view of the clip of the invention; 
       FIG. 4  is a side view of the clip; 
       FIG. 5  is a plan view of the clip; 
       FIG. 6  is a side elevational view of a known drop clip assembly; and 
       FIG. 7  is a side edge view of the known drop clip assembly. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A system  10  for suspending a pair of grid tees  11  in a uniformly spaced parallel arrangement is shown in  FIG. 1 . The grid tees  11 , typically, are main tees with a generally conventional construction. Each of the tees  11  has lower flange portions  12  and a generally vertical web or stem  13  which includes, adjacent its upper edge, a reinforcing bulb  14 , as is customary. Typically, the grid tees are roll formed of sheet metal stock. The grid tees are suspended from a plurality of structural channels  16 . Only one channel  16  is illustrated in  FIG. 1 , but it will be understood that a plurality of such channels  16 , typically, spaced parallel to one another, exist in a common plane spaced above the plane of the grid tees  11 . The channel  16  can be suspended in a building from the above floor or other superstructure existing above by means of suspension rods, wires, or the like. 
     FIGS. 6 and 7  illustrate a commercially available “drop clip” assembly  17  that includes a main body  18  and a locking channel or cap  19 . The main body  18  is a sheet metal stamping with a generally rectangular peripheral profile. A downwardly extending tab  20  works with the throat  21  to form a hook that captures the channel  16 . Adjacent its upper end, the body  18  has a rectangular throat  21  sized to provide a working clearance around the periphery of the structural channels  16 . Adjacent its lower end, the body  18  has a pair of parallel vertical slots  22  that leave three depending legs  23 - 25 . Outboard legs  23 ,  25  are bent slightly below the plane of the drawing of  FIG. 6 , while a central leg  24  is bent slightly above the plane of  FIG. 6 . At their lower ends, the legs have channel shape formations  27 ,  28 , that are configured to normally embrace the reinforcing bulb of a conventional grid tee. The locking channel cap  19  has a central slot in its web that enables it to slide vertically on the clip body  18 . When the locking channel cap  19  is manually forced downwardly over the legs  23 - 25 , including the channel formations  27 ,  28 , the channel formations are forced towards the central plane of the upper portion of the body  18  ( FIG. 2 ). A lanced formation  29  on the central leg  24  serves to lock the locking channel cap  19  in position over the leg channel formations  27 ,  28 . With the clip assembly  17  being manipulated onto a respective channel  16  so that it is received in the throat  21 , a section  31  of the body  18  can be bent upwardly to trap the clip assembly onto the channel. 
   A clip  36  of the invention serves to suspend the grid tees  11  from the drop clip body  18  and, therefore, from the structural channel  16  to which the drop clip assembly  17  is attached. The clip  36 , in the illustrated form, is a sheet metal stamping having the general form, when installed, of an inverted rectangular pan. The corners of the clip  36  are notched as required for receiving the bulbs  14  of the grid tees  11 . More particularly, the clip  36  has a generally planar, rectangular main section  37  from which depend downwardly bent opposed flanges  38 ,  39  and  41 ,  42 . The flanges  38 ,  39  are mirror images of one another and each includes an inwardly bent tab  46  spaced vertically below the main section  37  a distance at least equal to and preferably slightly greater than the vertical height of the reinforcing bulb  14  of a grid tee. Another flange  41 , extending transversely between the imaginary planes of the flanges  38 ,  39 , includes a pair of tabs  47  spaced from the plane of the main section  37  a distance equal to or slightly greater than the height of a reinforcing bulb  14 . The flanges  41  and  42  serve to stiffen the main section  37  of the clip  36  and keep it in a planar configuration under normally expected service conditions. The horizontal lengths of the flanges  41 ,  42  are somewhat less than the inside dimension between the opposed flanges  38 ,  39  so that, as shown in  FIG. 2 , there is room, preferably with a slight clearance, for the grid tee bulbs  14  to be received between the surface of a flange  38 ,  39 , and adjacent vertical end edge surfaces  51 ,  52  on the flange  41 . The inside dimension spacing of the surfaces of the flanges  38 ,  39  and the spacing between the vertical edge surfaces  51 ,  52 , are determined by the desired center-to-center distance between the grid tees  11  and the width of the reinforcing bulbs  14 , typically the latter being nominally ¼″. As suggested in  FIG. 2 , the upper edge surfaces  46   a,    47   a  of the tabs  46 ,  47  are spaced from the lower surface of the main section  37  a distance sufficient to receive the bulbs  14  of the grid tees. For illustrative purposes, end areas of the flange  41  and tabs  47  are shown in  FIG. 2 , ignoring the fact that the plane of the section of  FIG. 2  is technically behind these areas. 
   Disposed on opposite sides of an imaginary vertical mid-plane transverse to its length, the clip  36  has a pair of elongated transverse slots  53 . In the illustrated example, the slots  53  extend across substantially the full width of the clip main section  37 . The slots  53  are spaced from one another to leave a central land portion  54  that, preferably, has a width equal or substantially equal to the width of a conventional reinforcing bulb  14 , for example, nominally ¼″. The slots  53  are sufficiently wide and long to allow the free passage therethrough of the channel formations  27 ,  28  of the drop clip legs  23 - 35 . 
   The clip  36  is joined and locked, i.e. coupled, to the drop clip assembly  17  in the following manner, conveniently at the job site by the grid installer without tools. The drop clip legs  23 - 25 , in their laterally spread condition shown in  FIG. 7 , are inserted through the slots  53  so that in-turned flanges  57 ,  58  of the channel formations  27 ,  28  underlie the land  54  of the main clip section  37 . Thereafter, the locking channel cap  19  is forced downwardly relative to the drop clip body  18  so as to force the legs  23 ,  25  towards the central leg  24  and vice versa thereby trapping the land  54  in the channel formations  27 ,  28  above the flanges  57 ,  58 . When the channel cap  19  fully contacts the channel formations  27 ,  28 , it is locked in this position by the lance or lock  29 . As a consequence, the drop clip assembly  17  and paired tee clip are securely fixed together. Study of  FIGS. 1 and 2  shows that the interconnection of the clips  17  and  36  is symmetrical about imaginary vertical planes, one at a mid-plane through the thickness of the main body  18  of the drop clip and another perpendicular to the plane of the main body midway between its vertical edges. This results in a symmetrical support of the paired tee clip  36  which, in turn, assures that each of the four tabs  46 ,  47  of the clip  36  at their upper surfaces  46   a,    47   b  are effective in supporting the vertical load on the respective grid tee bulbs  14 . It will be appreciated that the clip  36  in concert with identical clips spaced along the lengths of a pair of grid tees  11  can precisely horizontally space the pair of grid tees with minimal skill and effort expended on the part of the installer. The length of the clip  36 , i.e. its extent on each side of the plane of the drop clip main body  18 , can be adjusted to suit a particular installation as would ordinarily be determined by an architect, for example. The space between the parallel paired grid tees  11  can be utilized for lighting fixtures, HVAC air boots, sprinkler heads, speakers and other utilities and appliances. 
   It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.

Summary:
A clip for accurately and quickly suspending pairs of spaced parallel grid main tees from superadjacent structural channels. The clip works with a separate drop clip that hooks over and depends from the structural channel. The paired main tee clip has a central body region configured like a conventional grid tee bulb thereby enabling the paired main tee clip to mate with the drop clip in the same way the drop clip mates with a conventional grid tee bulb thereby achieving a system that is cost-effective in manufacture and installation.