You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to suspended ceilings and, in particular, to improvements in tee components used to construct a metal grid for such ceilings. 
       PRIOR ART 
       [0002]    Suspended ceilings usually comprise a rectangular grid formed by spaced parallel main runners or tees and cross runners or tees extending perpendicularly between the main runners. The cross tees typically have end connectors that mate with identical connectors of other cross tees being joined end-to-end. The cross tee joints are made in a slot provided in the main tees. Where small grid modules are used in a ceiling construction, the cross tees can also be slotted to receive end connectors of other cross tees. Grid tees are typically made of roll-formed metal sheet stock and the gauge of the sheet stock is varied so that a tee is of adequate strength for the service it is expected to fulfill but, for costs reasons, not excessive. Also for reasons of economy, a manufacturer typically only uses one end connector configuration for all of its cross tee constructions regardless of the gauge or thickness of the stock used to make a slotted tee. 
         [0003]    A problem can exist where the same cross tee connector is used for all of a manufacturer&#39;s slotted tees. A lighter gauge slotted tee will have a tendency to be loose in the fit provided for it by a cross tee connector. This looseness adversely affects the feel of the joint to the installer and can potentially affect the appearance of the grid as well as the manner in which other components of the ceiling are received and/or are supported by the grid. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention improves the fit of standardized cross tee connectors when received in slots of tees with different gauge thickness for various duty ratings and/or spans. The invention involves the concept of producing grid tees with a range of service duty, reflected in the use of various gauge sheet stock, that exhibit an effective uniform thickness at their cross tee slots. More specifically, the invention comprehends locally altering a grid tee in the area of its cross tee receiving slot or slots so that the grid tee has a uniform effective thickness at these area(s) that can be standardized across a manufacturer&#39;s range of tee load ratings. 
         [0005]    In a preferred embodiment, a grid tee is permanently stamped with an indentation or dimple adjacent the cross tee slot and the connector has a lead edge area arranged to seat against the bottom of the indentation. The bottom of the indentation of tees made of different gauge thickness are formed with the same spacing from the center plane of the tee. Since the connector registers against it, this indentation bottom surface serves to establish the effective thickness of the slotted tee and in accordance with the invention a tee has the same dimension regardless of the actual gauge of material forming the tee. Ideally, the indentation is laterally offset, with reference to a view of the side of the tee, from the center of the slot so that the material displaced from the indentation for one connector does not substantially affect a similarly offset indentation for an opposing connector on the opposite side of the tee. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an exploded fragmentary perspective view of a slotted tee and a pair of cross tees with end connectors to be joined in the slot of the tee; 
           [0007]      FIG. 2  is an elevational view of the end connectors connected in the slot of the slotted tee of  FIG. 1 ; 
           [0008]      FIG. 3  is an elevational view of the end connectors connected in a slot of a conventional tee; 
           [0009]      FIG. 4  is a fragmentary elevational view of the end connectors of a pair of cross tees joined in the slot of the tee of  FIG. 1 ; and 
           [0010]      FIG. 5  is a cross sectional view of the slotted tee taken in the horizontal plane view indicated at  5 - 5  in  FIG. 4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0011]    Referring now to the figures, there is shown a small section of a suspended ceiling grid  10  at an intersection of tees  11 ,  12  (exploded in  FIG. 1  for clarity). A slotted tee or runner  11  represents a main tee, which typically is  10  or  12 ′ in length (or metric equivalent) or a shorter cross tee. A main tee will have numerous regularly spaced identical slots  13  while a cross tee will have relatively few slots  13  or no slots at all. In various views herein, two opposed cross tees  12  intersect the slotted tee  11  at the slot  13 . The cross tees  12  are assembled with end connectors  14  that, in a known manner, lock together when they are both properly inserted in a slot  13 . U.S. Pat. Nos. 5,517,796 and 5,761,868, incorporated herein by reference, disclose the general features of the end connector or clip  14 . While not shown, but known in the industry, the cross tees  12  can have slots and be intersected by still other cross tees in the grid of the ceiling. 
         [0012]    The tees  11 ,  12  are typically made of roll-formed sheet metal, usually steel that can be a hot-dipped galvanized product, and less frequently aluminum. The tees  11 ,  12  are symmetrical about a central or medial vertical plane and include, usually, a lower flange  16 , a vertical web  17 , and an upper hollow reinforcing bulb  18 . Normally when a tee is roll-formed of sheet stock, the web is a double layer of a sheet. 
         [0013]    Depending on the duty or load rating of a tee  11 ,  12  and, if it is a cross tee  12 , its span, the gauge of the metal sheet varies. By way of example, the thickness of a web  17 , i.e. the sum of the thickness of two layers if it is a double layer, can range between 0.050″ to 0.019″ (or metric equivalent). 
         [0014]    The end connectors  14  form a connector-to-connector lock when they are inserted into the same slot  13  from opposite sides of the tee  11 . The lock is actually a double lock with a lock being established on each side of a slotted tee  11  by a rearward facing edge  21  of a projection  22  and a rearward facing edge  23  of an opening  24  of the mating connector. Interlocking between the connectors  14  is precisely dimensionally controlled so that dimensional variations are not multiplied in an expansive ceiling grid. 
         [0015]    It is desirable that the slotted tee  11  be constrained by the cross tees  12  through the connectors  14  so that the slotted tee  11  is prevented from shifting laterally and/or twisting longitudinally, i.e. about an axis parallel to its longitudinal axis. To be commercially competitive, tees are manufactured with different strengths to meet industry or government standards while not unduly exceeding these standards with unnecessary material content. To satisfy this economic constraint, a manufacturer, inter alia, uses different gauge (thickness) material to construct the tee, the gauge being heavier the greater the duty rating or load capacity of the ceiling grid. Another constraint on a manufacturer is the need to use the same end connector configuration for any cross tee  12  regardless of the duty rating of the grid. 
         [0016]    The requisite variation in the web thickness of conventional tees and the need for a single end connector or clip configuration has been problematic. If the connector is proportioned to fit thick webs, slotted grid tees with thin webs are loosely held by the connectors. If a connector would be proportioned to fit closely with a conventional slotted tee with a thin wall web, it would not lock with a mating identical connector on a heavy wall slotted tee because the thicker web would hold the connectors apart. 
         [0017]    The invention solves the problem of a loose fitting slotted tee by locally modifying the grid tees in the web area of the slot so that regardless of the gauge thickness of the material of their web, they present the same or nearly the same effective thickness to the connectors. Preferably, according to the invention, this is done by permanently displacing material adjacent a slot so that the plane of a surface of the displaced area abutted by a connector has the same or nearly the same spacing from the center of the web as corresponding areas adjacent the slots of grid tees with webs of other thickness. More specifically, web material is permanently displaced by a stamping operation to form an indentation  26 . A surface  27  of a base of the indentation  26  has a predetermined distance D ( FIG. 5 ) from a center plane  29  of the web  17 . The indentation  26  is asymmetrical or offset to the left from a center line through the slot  13 . A lead edge  31  of a connector provided by a projection  32  on a laterally offset flange  33  is aligned with the indentation  26  and abuts the indentation bottom or base surface  27  to index the position of the connector  14  when it is fully installed. The indentation  26  is of sufficient area to receive the cross section of the projection  32  so that the projection is the exclusive element that determines the relative position of a cross tee to the slotted tee. As shown most clearly in  FIG. 5 , an indentation  26  is formed at each side or face  34  of the web  17 . The indentations  26 , ideally, are offset from the center line of the slot  13  a sufficient distance such that they do not overlap. Dimensional tolerances of and forces on tooling used to produce the indentation surfaces  27  are less critical than would be the case where the indentations of both sides  34  of the web  14  overlapped one another. 
         [0018]    The predetermined distance D of the indented surface  27  from the center plane  29  can be set at the same nominal dimension as is the outer surface of the thinnest web in a manufacturer&#39;s product line so that these lighter duty tees need not be stamped with an indentation. This is the condition illustrated in  FIG. 3 . Alternatively, a manufacturer may choose to set the nominal dimension at one corresponding to a medium duty web and, therefore, allow a lighter duty web to have a slight but acceptable clearance between a pair of joined connectors. 
         [0019]    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. For example, the tees can be configured with the indentation at the same location centered on the slot center line on both sides of a web. Still further, for example, the tees with lighter gauge (thinner webs) can be plastically deformed in the area of a cross tee slot to have the effective thickness of a heavier duty thicker web and the connectors can be configured to engage such area. The invention is applicable to tees with a single layer web and to tees having different flange configurations or bulb configurations than that illustrated.

Summary:
Producing grid tees with a range of service duty, reflected in the use of various gauge sheet stock, that exhibit an effective uniform thickness at their cross tee slots by locally altering a grid tee in the area of its cross tee receiving slot or slots so that the grid tee has a uniform effective thickness at these area(s) that can be standardized across a manufacturer&#39;s range of tee load ratings. Preferably, a grid tee is permanently stamped with an indentation or dimple adjacent the cross tee slot and a cross tee connector has a lead edge area arranged to seat against the bottom of the indentation.