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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     This invention relates to enclosures of the type used in industrial electrical and hydraulic systems and the like, and more particularly to an improved fastener for attaching removable access panels in such enclosures. 
     BACKGROUND OF THE INVENTION 
     Control components, wiring, and plumbing in industrial electrical and hydraulic control systems are often mounted in cabinet-like enclosures. Such enclosures typically include a frame having a flange for attachment of one or more removable access panels. Each access panel typically includes a number of quick-release fasteners installed through holes in the panel for attaching the panel to the flange. 
     Such quick-release fasteners typically include a retaining screw having a shaft section defining an axis. One end of the retaining screw is formed into a head having a larger outer diameter than the shaft of the screw, and including a slot, recess, flats, or knurling so that the screw may be installed and removed by hand or with common hand tools. The opposite panel retaining end of the screw is typically formed to provide male or female screw threads, an L-shaped form, or some other type of quick-attach retainer profile, cooperating with the flange or a mating thread, etc., attached to the flange for securing the access panel to the frame of the enclosure. 
     The fastener also typically includes a bushing having an outer profile which includes a first section shaped for insertion through a hole in the panel, a shoulder for positioning the bushing in the panel, and a bore extending through the bushing about the axis to receive the shaft with the head of the retaining screw adjacent the shoulder on the outside of the panel, and the opposite panel retaining end on the inside of the panel. The bushing is typically secured within the hole by a C-ring which snaps into a groove of the bushing inside of the panel after the bushing is inserted through the hole. It is common in such fasteners to have the head and panel retaining inner end of the retaining screw larger in diameter than the bore of the bushing, or otherwise configured such that the screw is held captive within the bushing. 
     In some fasteners, a spring is also provided between the head of the screw and the shoulder of the bushing to facilitate installation and removal of the panel by pulling the panel retaining end of the screw away from the flange after disengagement. 
     Inherent problems associated with the manufacture and use of prior art quick-release fasteners of the type described above increase the initial and life cycle cost of the fasteners and enclosures in which they are used. Performance and aesthetic desirability of the enclosures is also reduced by the inherent problems associated with the use of the prior art fasteners. 
     Using C-rings for retaining the fastener in the access panel creates several problems. The initial labor and part cost is increased by the need to stock, handle, and install the separate C-ring. The risk of dropping a C-ring into the enclosure during installation, operation, or maintenance activities is undesirable. There is also an aesthetic problem, in that unless the C-rings clamp the bushing of the fastener tightly against both faces of the panel, the fasteners may rattle when the panel is removed, giving a customer the impression of sloppy workmanship and shoddy design. To alleviate this problem, the bushings can be closely matched to a given panel thickness, but where several different panel thicknesses are used by a manufacturer, perhaps even on the same enclosure, this requires a different fastener configuration for each panel thickness. 
     Prior quick-release fasteners of the type described above having a head and panel retaining end configured to be larger in diameter or otherwise shaped so as to not slide through the bore of the bushing of the completed fastener are difficult to manufacture. Because neither the head nor panel retaining end of the retaining screw will fit through the bushing, the bushing must be installed on the shaft section of the retaining screw during manufacture prior to forming the head or forming the panel retaining end of the retaining screw. Where the fastener must ultimately be plated, or where a spring is utilized between the head and shoulder of the bushing, the necessity of installing the bushing midway through formation of the screw is highly undesirable. 
     It is an object of my invention, therefore, to provide an improved enclosure through the use of an improved quick-release fastener for access panels of the enclosure. Other objects of my invention include providing: 
     (1) a fastener that is more readily manufactured than prior fasteners at a lower cost; 
     (2) a fastener that is self-retaining; 
     (3) a fastener that is self-retaining in panels of several different thicknesses; 
     (4) a fastener in which the component parts can be separately manufactured and subsequently assembled following completion of all manufacturing operations on the various component parts; 
     (5) a bushing which can be installed on the shaft section of a retaining screw of a fastener following completion of all manufacturing steps for the retaining screw; and 
     (6) a fastener which can be retrofitted into existing panel and enclosure designs to improve their desirability. 
     SUMMARY OF THE INVENTION 
     My invention provides such an improved enclosure and solves the problems defined above through the use of an improved quick-release fastener. According to one aspect of the invention, the improved quick-release fastener includes a bushing having an outer profile including a first section shaped for insertion through a hole in an access panel of an enclosure, a shoulder and a resilient tang axially spaced from the shoulder for retaining the bushing in the panel, and a bore extending through the bushing about an axis for receiving a shaft section of a retaining screw of the quick-release fastener. In preferred embodiments of this aspect of my invention, the tang includes a serrated surface configured to bear against an inner surface of the access panel, with the serrations having notches shaped for receipt of the inner surface of panels of several thicknesses. According to another aspect of my invention, the improved quick-release fastener utilizes a bushing comprised of two segments separable along a plane passing through the axis of the bore of the bushing. In preferred embodiments, the two segments include corresponding male and female alignment formations for aligning the bushing about the bore. In a highly preferred embodiment, the two segments of the bushing are identical. 
     Other aspects and advantages of my invention will be apparent from a review of the following drawings and detailed description of exemplary embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exemplary embodiment of an enclosure according to my invention; 
     FIGS. 2 and 3 illustrate detailed features of the embodiment of FIG. 1; and 
     FIGS. 4-6 illustrate alternate embodiments of possible panel retaining ends for a retaining screw in a quick-release fastener according to my invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an exemplary embodiment of an enclosure  10  according to my invention. The enclosure  10  includes a frame  12  having a flange  14  for attachment of a removable panel  16 . The panel  16  includes a hole  18 , and a quick-release fastener  20  retained in the hole  18 , as described in detail below, for attaching the panel  16  to the flange  14  of the enclosure  10 . 
     The fastener  20  includes a retaining screw  22  having a shaft section  24  defining an axis  26 . The retaining screw  22  includes a head  28  at an outer axial end of the shaft  24 , and an L-shaped opposite inner axial panel retaining end  32  of the shaft section  24  for engaging the flange  14 . The shaft section  24  is located intermediate the head  28  and the latch  32 . The head  28  of the retaining screw  22  includes a slot  30  for receipt of a screwdriver or other such tool for turning the retaining screw  22 . Although FIG. 1 illustrates a slot  30  for receipt of a standard flat-bladed screwdriver, the head  28  of the screw  22  could also be configured to be compatible with other types of installation tools such as Phillips screwdrivers, hex head Allen wrenches, mechanic&#39;s wrenches, or even knurled for providing an enhanced finger grip or configured like a thumb screw such that the screw could be turned without the need for a tool. 
     As shown in FIGS. 1-3, the fastener  20  further includes a bushing  34  having an outer profile including a first section  36  shaped for insertion through the hole  18  in the panel  16 . The bushing  34  includes a shoulder  38  bearing against a first or outer surface  40  of the panel  16  for positioning the bushing  34  in the hole  18  of the panel  16 . The bushing includes a bore  42  extending through the bushing  34  about the axis  26  for receiving the shaft section  24  of the screw  22 , with the head  28  of the screw  22  adjacent the shoulder  38 . 
     The bushing  34  includes two identical bushing segments  44  separable along a plane  46  passing through the axis  26  of the bore  42 . The bushing segments  44  include corresponding male and female alignment formations in the form of projections and recesses  48 , 50  for aligning the bushing  34  about the bore  42 . The bushing  34  further includes a recess  52  centered on the axis  26  and opening toward the head  28  for receipt of a spring  54  extending from the shoulder  38  toward the head  28  of the screw, for biasing the shaft section  24  of the retaining screw along the axis  26  of the bore  42  in a direction away from the shoulder  38 . 
     The bushing  34  further includes a pair of resilient tangs  56 , one in each bushing segment  44 . The tangs  56  are axially spaced from the shoulder  38  of the bushing and configured to be resiliently displaced radially inward as the bushing  34  is inserted into the hole  18  of the panel. The tangs  56  include serrations  58  having a plurality of notches  60  shaped for receipt of a second face  62  of the panel  16 . The notches  60  in the serrations  58  of the tangs  56  are shaped such that the bushing  34  can be utilized in panels having several different thicknesses t, with the notches being axially spaced from the shoulder  38  and configured such that for each incremental thickness t, a notch is available for gripping the second or inside face  62  of the panel  16 . 
     Those having skill in the art will recognize that through use of the split bushing  34  with integral tangs  56  configured to accommodate a number of different panel thicknesses t, my invention provides solutions to the problems detailed above and a number of advantages when used in the manufacture and operation of the type of enclosures described herein. Having the bushing  34  be separable, allows all pieces of the quick-release fastener  20  to be manufactured independent of each other, and brought together only at the assembly stage, thereby eliminating the manufacturing problems inherent in prior quick-release fasteners. The corresponding male and female alignment formations  48 , 50  facilitate assembly and installation. Forming the bushing  34  of two identical segments  44 , reduces manufacturing and inventory costs. The tangs  56  eliminate the need for the separate C-rings utilized in prior quick-release fasteners, thereby reducing both initial assembly and operating cost, and reducing the risk of a C-ring being dropped into the enclosure. The serrations  58  and notches  60  in the tangs  56 , and the overall configuration of the tangs  56  which allows the fastener  20  to be quickly inserted by simply pushing it into the hole  18  in the panel  16 , and to be held fast there in panels of varying thickness to reduce rattling, provides advantages reducing the cost and improving the aesthetic desirability of the enclosure. 
     Although I have described my invention in terms of various exemplary embodiments thereof, those skilled in the art will recognize that there are a number of variations that can be made without departing from the scope of my invention as defined by the appended claims. For instance, as illustrated in FIGS. 4-6, the inner axial panel retaining end  32  of the shaft section  24  of the retaining screw  22  can be formed into a male thread  64 , or a female thread  66 , or as one part  68  of a quick-attach retainer to mate respectively with a cooperating female thread  65 , male thread  67 , and second part of a quick-attach retainer attached to the flange  14 . It is understood, therefore, that the spirit and scope of the appended claims should not be limited to the specific embodiments described and depicted herein.

Summary:
Performance and aesthetic attractiveness of industrial enclosures of the type used to house electrical and hydraulic equipment are enhanced through use of an improved quick-release fastener for attaching removable access panels of such enclosures. The improved fastener includes a split bushing with integral retaining tangs configured for retaining the quick-release fastener in access panels having different thicknesses.