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FIELD OF THE INVENTION 
   The present invention relates generally to rails, and more particularly to rails used in fences and other barriers. 
   SUMMARY OF THE INVENTION 
   The rail of the present invention comprises a channel element which features a platform having opposed first and second lateral edges, a first side wall which depends from the first lateral edge of the platform, and a second side wall which depends from the second lateral edge of the platform. The platform and the first and second side walls define boundaries of a rail channel. The channel element further comprises a tray holder adapted to slidably support a tray element within the rail channel, while restricting its movement toward or away from the platform. The rail may further comprise a tray element supportable on the tray holder in an installed position within the channel element, with the tray element and the channel element defining boundaries of a retainer channel. 
   The present invention further comprises a fence comprising a plurality of the above-described rails and a plurality of vertically disposed posts. Each adjacent pair of posts supporting the opposite ends of a plurality of rails. The fence further comprises a plurality of pickets, with each picket being laterally traversed by at least one retainer passage. The fence further comprises an elongate retainer element which is positioned within the retainer channel such that it passes through the aligned retainer passages of the pickets. 
   The present invention further comprises a kit comprising a plurality of the above-described rails, and further comprising a plurality of posts and a plurality of pickets. 
   The present invention further comprises a method of making the above-described rail, comprising forming the channel element from an extrudable material by an extrusion process, and forming the tray element from an extrudable material by an extrusion process. 
   The present invention further comprises a method of assembling the above-described fence, comprising installing a plurality of pickets into a rail, such that their retainer passages are aligned. A retainer element is then inserted into the retainer channel, and through the aligned retainer passages of the installed pickets. These steps are repeated for each additional rail which will support the pickets. Each rail is then secured at its opposite ends to an adjacent pair of posts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front elevational view of a section of a fence formed from the rail of the present invention. The section has been shown fragmentarily to indicate indeterminate length. The supporting terrain and substrates are shown in cross section. 
       FIG. 2  is a top plan view showing the channel element of the rail of the present invention. 
       FIG. 3  is a cross-sectional view of the channel element shown in  FIG. 2 , taken along line  3 — 3 . 
       FIG. 4  is a top plan view showing the tray element of the rail of the present invention. 
       FIG. 5  is a cross-sectional view of the tray element shown in  FIG. 4 , taken along line  4 — 4 . 
       FIG. 6  is a cross-sectional view of the rail of the present invention in an assembled state, showing the tray element installed within the channel element. 
       FIG. 7  is a perspective view of a partial section of fence which includes two rails of the present invention. The channel element of the upper rail has been partially cut away, in order to display other components of the fence. The pickets and rails have been shown fragmentarily to indicate indeterminate length. Grommets on the left-hand picket have been shown in an unseated position, to better display other components. The retainer element in each rail is not fully installed within the rail, to better illustrate the assembly process. 
       FIG. 8  is a front elevational view of a section of a fence, the upper rail of which comprises another embodiment of the rail of the present invention. The section has been shown fragmentarily to indicate indeterminate length. The supporting terrain and substrates are shown in cross section. 
       FIG. 9  is a top plan view of the upper rail shown in  FIG. 8 . 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , the present invention comprises a fence, generally designated by reference numeral  10 . The fence  10  preferably comprises a plurality of adjacent sections, such as the sections  12  and  14 . Each section comprises a pair of adjacent vertical posts  16 . Preferably, the fence  10  is configured so that the same single post  16  may be shared by two adjacent sections, as shown in  FIG. 1 . 
   Preferably, the posts  16  are of identical construction. Each of the posts  16  is securely anchored at its lower portion into a substrate  18 , such as an underground mass of concrete. The substrates  18  are preferably disposed in spaced relationship, with a separate substrate preferably supporting each post  16 . The posts  16  are situated along the boundary of the area to be enclosed by the fence  10 , with a post spacing which is adequate to impart strength to the fence  10  and to securely anchor other fence components. In one preferred embodiment, adjacent posts comprising a section are separated by a distance of no greater than 8 feet. 
   The above-ground height of each post  16 , in its installed configuration, is preferably sufficient to impede or deny access by a human or other intruder. In preferred embodiments, the above-ground height of each post  16  is between 3 and 10 feet. The upper end of each post  16  may be provided with a round top, as shown in  FIG. 1 . Alternately, a flat post top may be used, or a top which has been formed into pointed or sharpened configuration, such as a spear or spike. 
   Each of the posts  16  is preferably formed from a strong and durable material, and more preferably from a material which is relatively lightweight and extrudable as well. Preferred materials include aluminum, aluminum alloys, and plastics such as polyvinyl chloride. One particularly preferred material is 6005-T5 aluminum alloy. Preferably, the post  16  is formed in a die by an extrusion process. After the post  16  has been formed, a polyester powder coating is preferably provided in order to enhance corrosion resistance of the post. 
   The post  16  is tubular in construction, and preferably is characterized by a rectangular, and more preferably, a square cross-section. The post  16  may be hollow, or may include a core or other structure to increase its strength. In a preferred embodiment, the post  16  is characterized by an internal wall which interconnects two opposing side walls of the post  16 , thereby defining a double box cross-sectional structure. In a preferred embodiment, the side walls of the post  16  are characterized by a thickness of 0.06 inches or more, and a width of between 2.5 and 4 inches. 
   With continued reference to  FIG. 1 , each section of the fence  10  further comprises a plurality of elongate rails  20 . Each rail  20  is preferably formed from two separate and discrete components: a channel element  26 , shown in  FIGS. 2 and 3 ; and a tray element  28 , shown in  FIGS. 4 and 5 . Each of these components of the rail  20  is preferably formed from a strong and durable material, and more preferably from a material which is relatively lightweight and extrudable as well. Preferably, each component of the rail  20  is separately formed in a die by an extrusion process. After a rail component has been formed, a polyester powder coating is preferably provided in order to enhance the component&#39;s corrosion resistance. 
   The present invention is well-adapted to rails formed from materials which are not readily susceptible to conventional roll forming, such as aluminum and its alloys. Preferred materials for the rail  20  include aluminum, aluminum alloys, and plastics such as polyvinyl chloride. Particularly preferred materials are 6005-T5 aluminum alloy (for channel elements) and 6063-T5 aluminum alloy (for tray elements). 
   With reference to  FIGS. 2 and 3 , the channel element  26  comprises an elongate structure having a generally U-shaped cross section. The channel element  26  is characterized by a elongate planar platform  30  having a first lateral edge  32  and an opposed second lateral edge  34 . A plurality of collinear, longitudinally spaced, picket openings  35  are formed in the platform  30 . 
   A first side wall  36  depends from the first lateral edge  32 , and a second side wall  38  depends from the second lateral edge  34 . The platform  30  and side walls  36  and  38  define boundaries of a rail channel  40 . The first and second side walls  36  and  38  are preferably disposed in parallel planes, with each orthogonal to the plane of the platform  30 . Preferably, the base of each of the side walls  36  and  38  is provided with an inturned flange section  42  positioned within the rail channel  40 . Each flange section  42  is preferably characterized by a L-shaped cross section, and functions to enhance the strength of the channel element  26 . 
   As best shown in  FIG. 3 , the channel element  26  further comprises a tray holder  44  adapted to slidably support a tray element  28  within the rail channel  40 . The tray holder  44  preferably comprises a first runner element  46  projecting within the rail channel  40  from the first side wall  36 , and a second runner element  48  projecting within the rail channel  40  from the second side wall  38 . The runner elements are adapted to slidably receive and support a tray element  28  within the rail channel  40 , and further function to restrain movement of the tray element  28  away from the platform  20  towards the mouth  50  of the rail channel  40 . 
   Each of the runner elements  46  and  48  preferably each comprises an elongate flange having a L-shaped cross section. Each such flange preferably extends continuously and linearly along substantially the entire length of the channel element  26 . Alternately, either or both of the runner elements  46  and  48  may comprise a series of spaced collinear flanges, rather than a single elongate flange. The first and second runner elements  46  and  48  should be equidistant from the platform  20 . 
   With continued reference to  FIG. 3 , the tray holder  44  preferably further comprises a first stop element  52  projecting within the rail channel  40  from the first side wall  36 , and a second stop element  54  projecting within the rail channel  40  from the second side wall  38 . The stop elements  52  and  54  function to restrain movement of the tray element  28  toward the platform  20 . 
   Each of the stop elements  52  and  54  preferably comprises an elongate rib which extends continuously and linearly along substantially the entire length of the channel element  26 , in spaced relationship to an adjacent runner element. Alternately, either or both of the stop elements may comprise a series of spaced collinear ribs, rather than a single elongate rib. The stop elements  52  and  54  should be equidistant from the platform  20 , with each stop element situated nearer the platform  20  than its adjacent runner element. 
   The runner elements  46  and  48 , and the stop elements  52  and  54  cooperate to define a cage within which a tray element  28  may be slidably received and supported. While permitting easy insertion or withdrawal of the tray element  28  from the channel element  26 , this cage restricts movement by a received tray element  28  either toward or away from the platform  20 . 
   With reference to  FIGS. 4 and 5 , the tray element  28  comprises an elongate planar platform  56  having a first lateral edge  58  and an opposed second lateral edge  60 . The length of the platform  56  is preferably substantially the same as that of the platform  30  of channel element  26 , while its width should permit the platform  56  to be clearingly received within the rail channel  40 . 
   A plurality of collinear, longitudinally spaced, picket openings  62  are formed in the platform  56 . The picket openings  62  are preferably disposed so that, when the tray element  28  is installed in the channel element  26 , the center of each picket opening  62  is aligned with the center of a corresponding picket opening  35  formed in the channel element  26 , such that the line of alignment between the two centers is orthogonal to the planes of the platform  30  and platform  56 . 
   As shown in  FIG. 5 , the tray element  58  further comprises a first leg  64 , which depends from the first lateral edge  58  of the platform  56 , and a second leg  66  which depends  66  from the second lateral edge  60 . The first and second legs  64  and  66  are preferably disposed in parallel planes, with each orthogonal to the plane of the platform  56 . As shown in  FIG. 6 , the platform  56  and first and second legs  64  and  66  are sized to be clearingly received within the rail channel  40 , and within the cage defined by the runner elements  46  and  48  and stop elements  52  and  54 . 
   In one preferred embodiment of the rail  20 , the channel element  26  is characterized by a substantially square profile, with the platform  20 , first side wall  36  and second side wall  38  each having a width of 1.75 inches. The typical wall thickness of the tray element  28  in this embodiment is 0.12 inches. In the same embodiment, the width of the platform  56  of the tray element  26  is 1.481 inches, while the overall height of the tray element  26 , comprising the distance between the upper surface of the platform  56  and the base of either of the legs  64  and  66 , is 0.25 inches. The typical wall thickness of the tray element  28  in this embodiment is 0.08 inches. 
   With continued reference to  FIG. 6 , the rail  20  is assembled by sliding the tray element  28  into the tray holder  44  of the channel element  26 , until the entire length of the tray element  28  is within the rail channel  40 . In this installed position of the tray element  28 , the platform  56  of tray element  28 , and the platform  30  of channel element  26 , define boundaries of a retainer channel  68 . The retainer channel  68  is situated within the rail channel  40 , and extends along the length thereof adjacent the platform  30 . The portion of each of the side walls  36  and  38  which extends between the platforms  30  and  56  forms an additional boundary for the retainer channel  68 . 
   In an installed position, each of the assembled rails  20  extends between an adjacent pair of posts  16  comprising a section of the fence  10 , as shown in  FIG. 1 . Two brackets  22  are used to connect the respective ends of a rail  20  to a pair of adjacent posts  16 . Each bracket  22  is connected to the rail  20  by a fastener (not shown), such as a bolt or a screw. This fastener preferably extends through an aperture (not shown) in the bracket  22 , and through a registering aperture  70  formed in a side wall of the rail  20 , as shown in  FIG. 7 . 
   At least two rails  20  extend between each adjacent pair of posts  16 . While any plural number of rails may be provided for each section, either two rails, as shown in  FIG. 1 , or three rails, as shown in  FIG. 9 , are preferred. The length of each rail  20  should be sufficient to fully span the distance between the adjacent of pair of posts  16  which will support that rail  20 . A rail length of either 6 feet or 8 feet is preferred. 
   The rails  20  which extend between a given pair of posts are preferably disposed in parallel relationship. The incline of each rail  20  with respect to horizontal should substantially equal the incline of the terrain  24  on which pair of posts  16  supporting that rail  20  are installed. Thus, when a section  12  is positioned on horizontal terrain, as shown in  FIG. 1 , the rails  20  will be disposed substantially horizontally. 
   With continued reference to  FIGS. 1 and 2 , each section of the fence  10  further comprises a plurality of vertically disposed pickets  72 , preferably of identical construction. Each picket  72  is preferably formed from a strong and durable material, and more preferably from a material which is relatively lightweight and extrudable as well. Preferred materials include aluminum, aluminum alloys, and plastics such as polyvinyl chloride. One particularly preferred material is 6063-T6 aluminum alloy. Preferably, the picket  72  is formed in a die by an extrusion process. After the picket  72  has been formed, a polyester powder coating is preferably provided in order to enhance corrosion resistance. 
   Each picket  72  is tubular in construction, and preferably is characterized by a rectangular or, most preferably, a square cross-section. The picket  72  may be hollow, or may include a core or other structure to increase its strength. The cross-sectional dimensions of the picket  72  should permit it to be clearingly received through the picket openings  35  and  62 . In a preferred embodiment, the side walls of picket  72  are characterized by a thickness of 0.05 inches, and a width of 0.75 inches. As shown in  FIGS. 1 and 7 , the upper end of each picket  72  may be provided with a pointed or sharpened top, such as a spear or spike, as shown in  FIG. 1 . Alternately, each picket  72  may be provided with a flat or rounded top. 
   The length of each picket  72  is preferably approximately equal to the vertical above-ground height of the posts  16 . In preferred embodiments, each picket will have a length between 45 inches and 72 inches. In an installed position, the base of each picket  72  should preferably be situated no more than a small distance above the terrain  24  supporting the fence  10 , in order to prevent an intruder from traversing the gap between the base of the picket  72  and the terrain  72 . 
   The pickets  72  are preferably oriented in parallel relationship, with a separation distance between adjacent pickets  72  and between each post  16  and its adjacent picket  72 , which is sufficiently small to prevent an intruder from traversing the gap. In one preferred embodiment, the separation distance between the centers of adjacent pickets  72 , and between each post  16  and its adjacent picket  72 , is 4 inches or less. Between adjacent pairs of posts  16 , pickets  72  should be provided in sufficient number to assure that the separation distance between adjacent pickets  72 , or between a post  16  and an adjacent picket  72 , does not exceed the requisite distance. 
   With reference to  FIG. 7 , each picket  72  to be installed in a section of the fence  10  should be laterally traversed by a plurality of parallel, longitudinally offset, retainer passages  74 . The number of retainer passages  74  in each picket  72  preferably equals the number of rails  20  in the section. The relative position, orientation and size of each of the retainer passages  74  in each of the pickets  72  should be identical. 
   Each retainer passage  74  should cross the longitudinal axis of symmetry of the picket  72 , preferably along a path which is perpendicular to, and interconnects, two opposed sides of the picket  72 . The retainer passages  74  should be positioned on the picket  72  such that each retainer passage  74  may be aligned with a corresponding retainer channel  68  of a rail  20  in the section of fence  10 . The retainer passages  74  of a plurality of linearly aligned pickets  72  should be linearly alignable. 
   The present invention further comprises an elongate retainer element  76 , shown in  FIG. 7 , which connects a plurality of pickets  72  to a rail  20 . The retainer element  76  preferably comprises a rod formed from a strong a durable material, such as galvanized steel. The length of the retainer element  76  should be equal to, or slightly less than, the length of the rail  20 . In one preferred embodiment, the length of the retainer element  76  is between 0.75 inches and 2.00 inches less than the length of the rail  20 . The cross-sectional dimensions of the retainer element  76  should permit it to be clearingly received within the retainer channel  68 , and clearingly received within the retainer passage  74  of each picket  72 . In a preferred embodiment, the retainer element  76  is characterized by a circular cross-section, and a diameter of 0.125 inches. 
   Pickets  72  are installed on a rail  20  by extending the picket  72  through an unoccupied picket opening  62  of the tray element  28 , and through the aligned picket opening  35 , if any, in the channel element  26 , until the retainer channel  38  of the rail  20  is aligned with the retainer passage  74 . This step is repeated for each additional picket  72  to be installed on the rail  20 . The pickets  72  should be positioned on the rail  20  such that the retainer passages  74  of the pickets  72  are in linear alignment, as shown in  FIG. 7 . Once all pickets  72  have been positioned as required, a retainer element  76  is inserted into the retainer channel  68  and passed through the aligned retainer passages  74  of each of the pickets  72  to be installed on the rail  20 . 
   As shown in  FIG. 7 , the fence  10  preferably comprises a plurality of grommets  78 , which protect internal components of the fence  10  from water damage and corrosion. Each grommet  78  is seated in a picket openings  35 , and fills the region between the platform  30  and the picket  72 . The grommets  78  are preferably formed from a strong, flexible and water-resistant polymer, such as polyvinyl chloride, and are provided in a number equal to the number of picket openings  35  in the section. The grommets  78  are preferably installed by seating them in the picket openings of each rail  20  before installation of the pickets  72  into that rail. The final seated placement of a grommet  78  in the assembled fence  10  is shown at the right-hand picket of  FIG. 7 . 
   After the pickets  72  comprising a section of fence  10  have been installed on a first rail  20 , as described above, the same steps should be repeated for each additional rail  20  which will support the same pickets  72 . The result of this series of steps is a rail-picket framework. This rail-picket framework is then formed into a section of fence by securing each rail  20  of the framework at its opposite ends to an adjacent pair of posts  16 , as shown in  FIG. 1 . Additional sections of the fence  10  may be formed and installed by repeating these steps. 
   As shown in  FIGS. 2 and 4 , the length of each picket opening  62  formed in the tray element  28  preferably exceeds the length of the adjacent picket opening  35  with which it registers. The greater length of the picket openings  62  permits the pickets  72  to be positioned in a vertical orientation, even when the rails  20  are not horizontal, as may occur when the fence  10  is installed on non-horizontal terrain. 
   The picket-rail attachment in the fence  10  of the present invention is situated within the rail channel  40 , and thus is not exposed to the external environment. In addition to its aesthetic advantages, this internal connection promotes security, by denying an intruder or vandal any practical way of prying a picket  72  away from the rails  20 . At the same time, the retainer elements  76  and retainer channels  68  function much like latches, and prevent the pickets  72  from being forcibly withdrawn from the picket openings  35  and  62 . Because it is not exposed to the elements, the internal picket-rail connection is also less susceptible to corrosion and water damage. 
     FIG. 8  shows another embodiment of the fence of the present invention, generally designated by reference number  100 . Much as with the embodiment described with reference to  FIGS. 1–7 , each section of the fence  100  is formed a pair of adjacent vertical posts  102 , which support a plurality of parallel rails therebetween. The fence  100  comprises at least an upper rail  104  and a lower rail  106 . Preferably, the fence  100  further comprises an intermediate rail  108 , situated between upper rail  104  and lower rail  106 . The lower rail  106  and intermediate rail  108  are identical in construction to the rail  20  described with reference to  FIGS. 1–7 . 
   The upper rail  104  is formed from a channel element  110  and a tray element (not shown). The channel element  110  is identical to the channel element  26 , except that its platform  112  is unperforated, with no picket openings formed therein, as shown in  FIG. 9 . Because of absence of picket openings in the platform  112 , the pickets  114  of the fence  100  terminate within the rail channel of the upper rail  104 , as shown in  FIG. 8 , and no grommets are used. In contrast, in the fence  10  shown in  FIG. 1 , the pickets  72  terminate above the upper rail  20 . Other aspects of the construction and assembly of the upper rail  104 , including the tray element, and fence  100 , are identical to those described with reference to rail  20  and fence  10 . 
   The fence of the present invention may be assembled from, and the methods of the invention advantageously practiced with, a kit. The kit of the present invention preferably comprises a plurality of posts, preferably identical to the posts  16 . The posts  16  are preferably provided in a number sufficient to form the fence, or section thereof, to be installed. 
   The kit further comprises a plurality of rails  20 , with each rail  20  including a channel element  26 , a tray element  28  and a retainer element  76 . The rails  20  should be provided in the kit in a number sufficient to form the fence, or section thereof, to be installed. The kit should further comprise a plurality of brackets  22  and fasteners should for securing each rail  20  to an adjacent pair of posts  16 . The brackets and fasteners are preferably provided in a number sufficient to form the fence, or section thereof, to be installed. 
   The kit further comprises a plurality of pickets, preferably identical to the pickets  72 , preferably in a number sufficient for the fence, or section thereof, to be installed. 
   Changes may be made in the construction, operation and arrangement of the various parts, elements, steps and procedures described herein without departing from the spirit and scope of the invention as defined in the following claims.

Summary:
A two-part rail is formed from a channel element which includes internal runners and stops which form a tray holder. A separate tray element may slide into the channel element, where it is supported on and confined by the tray holder. The tray element and channel element define boundaries of a retainer channel. Pickets traversed by alignable retainer passages are inserted through registering picket openings in the channel and tray elements of a rail. The pickets are secured to the rail by inserting a rod-like retaining element into the retainer channel of the rail and through the aligned retainer passages of the pickets.