BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to a two-stage quarter turn fastener which is used to fasten adjacent panels to each other. 
     2. Description of the Prior Art 
     In the prior art, it is known to use a fastener to secure adjacent panels to each other. Quarter turn fasteners are frequently used, particularly when square apertures are formed in the panels. However, such prior art fasteners typically have not been able to accommodate a range of panel thicknesses. Moreover, such prior art fasteners typically have not been configured to remain fastened to a first panel without being fastened to the second panel. 
     Examples of prior art include U.S. Pat. No. 5,897,278 entitled “Turn Fastener”, issued on Apr. 27, 1999 to Frattarola; U.S. Pat. No. 5,011,356 entitled “Panel Fastener”, issued on Apr. 30, 1991 to Fernandez; U.S. Pat. No. 4,981,405 entitled “Fastener For Securing Panel-Like Members”, issued on Jan. 1, 1991 to Kato; U.S. Pat. No. 4,938,645 entitled “Tee Tree Fastener”, issued on Jul. 3, 1990 to Wollar; U.S. Pat. No. 4,810,147 entitled “Fastener for Plates”, issued on Mar. 7, 1989 to Hirohata; U.S. Pat. No. 4,762,437 entitled “Fastener”, issued on Aug. 9, 1988 to Mitomi; and U.S. Pat. No. 4,652,192 entitled “Expandable, Plastic Panel Fastener”, issued on Mar. 24, 1987. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a quarter turn fastener configuration which can engage panels over a range of thicknesses. 
     It is therefore a further object of the present invention to provide a quarter turn fastener which can engage two panels or a single panel. 
     It is therefore a still further object of the present invention to provide a quarter turn fastener which can be reliably and intuitively operated. 
     It is therefore a final object of the present invention to provide a quarter turn fastener which can be manufactured economically. 
     These and other objects are attained by providing a fastener assembly with two quarter turn fasteners. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein: 
     FIG. 1 is a side plan view of the first aspect of the double quarter turn fastener of the present invention. 
     FIG. 2 is a perspective view of the first aspect of the double quarter turn fastener of the present invention. 
     FIG. 3 is a top perspective view of the first aspect of the double quarter turn fastener of the present invention, shown in the unfastened configuration. 
     FIG. 4 is a top perspective view of the first aspect of the double quarter turn fastener of the present invention, shown in the fastened configuration. 
     FIG. 5 is a perspective view of the head of the first aspect of the double quarter turn fastener of the present invention. 
     FIG. 6 is a perspective view of the first aspect of the double quarter turn fastener of the present invention, shown in position with two panels, in the unfastened configuration. 
     FIG. 7 is a perspective view of the first aspect of the double quarter turn fastener of the present invention, shown in the installed and fastened configuration with two panels. 
     FIG. 8 is a perspective view of the interior of the first stage of the second aspect of the double quarter turn fastener of the present invention. 
     FIG. 9 is a perspective view of the second stage of the second aspect of the double quarter turn fastener of the present invention. 
     FIG. 10 is a side plan view, partially in phantom, of the installed first and second stages of the second aspect of the double quarter turn fastener of the present invention. 
     FIG. 11 is a side plan view of the first and second stages of the second aspect of the double quarter turn fastener of the present invention, installed on a single thin panel. 
     FIG. 12 is a side plan view of the first and second stages of the second aspect of the double quarter turn fastener of the present invention, installed on a thin panel and a thick panel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, FIGS. 1-7 disclose various views of the first aspect of the fastener assembly  10  of the present invention. Fastener assembly  10  includes first stage  12  and second stage  14 . First stage  12  and second stage  14  are typically made from molded plastic, although those skilled in the art may recognize a range of equivalent substitutions. 
     First stage  12  includes disk-shaped head  16  with external surface  18  with, as shown in FIG. 5, L-shaped lands  20 ,  22 ,  24 ,  26  which form intersecting orthogonal grooves  28 ,  30  thereby forming a Phillips head-type configuration. First stage  12  further includes post  32  which rises from disk-shaped head  16  and terminates in distal end  34 . Locking flanges  36 ,  38  extend orthogonally from distal end  34 . Square-shaped seat  40  with sides  42 ,  44 ,  46 ,  48  is formed on interior side  50  of disk-shaped head  16 . Prongs  52 ,  54 ,  56 ,  58  are formed inwardly adjacently from sides  42 ,  44 ,  46 ,  48 , respectively, and extend obliquely outward therefrom and terminating in surfaces  52   a ,  54   a ,  56   a ,  58   a  which are generally parallel with disk-shaped head  16 . As can be seen from FIGS. 3 and 4, the exterior walls of prongs  52 ,  54 ,  56 ,  58  are aligned with the exterior walls of adjacent prongs thereby forming lines of a square generally at 45° angles with sides  42 ,  44 ,  46 ,  48  of seat  40 . 
     Second stage  14  has a generally square cross section when viewed from above, and includes chamfered lower corners  62 ,  64 ,  66 ,  68 . Additionally, second stage  14  includes a diagonally oriented channel  70  passing therethrough. Diagonally oriented channel  70  includes an enlarged central circular portion  72 . Diagonally oriented channel  70  allows locking flanges  36 ,  38  to pass through second stage  14 , with post  32  extending through enlarged central circular portion as shown in FIGS. 3 and 6. Pie-shaped locking pockets  74 ,  76  are formed adjacent to diagonally oriented channel  70 , extend generally radially from enlarged central circular portion  72 , and pass partially through second stage  14  and are bounded by floors  78 ,  80 . As shown in FIG. 3, this engaged but unlocked configuration causes chamfered corners  62 ,  64 ,  66 ,  68  to face surfaces  52   a ,  54   a ,  56   a ,  58   a  of square-shaped seat  40 . The configuration of FIGS. 3 and 6 allows second stage  14  to be rotated 45° about post  32  so that locking flanges  36 ,  38  are engaged within locking pockets  74 ,  76  to reach the locked configuration shown in FIGS. 4 and 7. In this locked position, chamfered corners  62 ,  64 ,  66 ,  68  are aligned with the corners of square-shaped seat  40 . 
     A typical installation procedure is illustrated in FIGS. 6 and 7. As shown in FIG. 6, first stage  12  is engaged but not fastened to second stage  14  (similar to FIG.  3 ). Head  16  is hidden behind first panel  100  with post  32  extending through square-shaped aperture  102  into which square-shaped seat  40  has seated. Post  32  further extends through rectangular aperture  202  in second panel  200  (the smaller side of rectangular aperture  202  being approximately equal in length to the width of second stage  14 ). Second stage  14  is thereafter rotated 45° to reach the locked configuration shown in FIGS. 4 and 7. During rotation of second stage  14 , chamfered corners  62 ,  64 ,  66 ,  68  progressively engage the edge of rectangular aperture  202  thereby allowing second stage  14  to engage a range of panel thicknesses. 
     FIGS. 8-12 disclose second aspect of fastener assembly  1010  which include first stage  1012  (FIG. 8) and second stage  1014  (FIG.  9 ). First stage  1010  includes circular head  1016  which, while not illustrated, typically includes an exterior Phillips-head type surface similar to that illustrated in first aspect of fastener assembly  10 . First stage  1010  includes central aperture  1018 , which as shown in phantom in FIG. 10 includes portion of slightly reduced diameter  1020  followed by portion of slightly increased diameter  1022  thereby forming inverted circular ledge  1024  therebetween. First stage  1012  further includes square-shaped seat  1026  bounded by four sides  1028 ,  1030 ,  1032 ,  1034 . Four prongs  1036 ,  1038 ,  1040 ,  1042  extend obliquely outwardly from inwardly adjacent from sides  1028 ,  1030 ,  1032 ,  1034  terminating in surfaces  1036   a ,  1038   a ,  1040   a ,  1042   a  on which hemispherically extending nubs  1044 ,  1046 ,  1048 ,  1050 , respectively, are formed. Additionally, upwardly extending lips  1052 ,  1054 ,  1056 ,  1058  (see FIGS. 8 and 10) are formed on the outermost radial areas of surfaces  1036   a ,  1038   a ,  1040   a ,  1042   a . As can be seen from FIG. 8, the exterior walls of prongs  1036 ,  1038 ,  1040 ,  1042  are aligned with the exterior walls of adjacent prongs thereby forming lines of a square generally at  450  angles with sides  1028 ,  1030 ,  1032 ,  1034  of square-shaped seat  1026 . 
     Second stage  1014  includes lower shaft  1062  with an annular ring  1064  which, as shown in FIG. 10, is inserted into central aperture  1018  of aperture  1018  of first stage  1012  thereby snap engaging inverted circular ledge  1024 . Second stage  1014  further includes upper hexagonal shaft  1066  (see FIG. 9) raised corners  1068 ,  1070 ,  1072 ,  1074  which are formed by walls extending obliquely upwardly from valleys  1076 ,  1078 ,  1080 ,  1082  which extend from the base of upper hexagonal shaft  1066  to the mid-points of sides  1084 ,  1086 ,  1088 ,  1090  of second stage  1014 . Raised corners  1068 ,  1070 ,  1072 ,  1074  further include upwardly extending prongs  1092 ,  1094 ,  1096 ,  1098 . 
     Fastener assembly  1010  is typically shipped in a configuration wherein hemispherically extending nubs  1044 ,  1046 ,  1048 ,  1050  align with raised corners  1068 ,  1070 ,  1072 ,  1074 . 
     FIG. 12 illustrates fastener assembly  1010  engaging a thin panel  1200 . Fastener assembly  1010  is inserted into a square aperture (not shown) in thin panel  1200  and given a quarter turn so that thin panel  1200  engaged between circular head  1016  and prongs  1036 ,  1038 ,  1040 ,  1042 . This allows fastener assembly  1010  to be fastened to a first panel and remain attached without the need for fastening a second panel. 
     FIG. 11 illustrates fastener assembly  1010  engaging a thin panel  1200  and a thick panel  1300 . Thick panel  1300  is placed over thin panel  1200  and fastener assembly  1010  fits through a square aperture (not shown) in thick panel  1300  which is offset 45° from the square aperture (not shown) in thin panel  1200 . Second stage  1014  is then turned a quarter turn from the configuration shown in FIG.  11 . Second stage  1014  rotates with respect to first stage  1012  thereby allowing the assembly to be completed. The configuration of the two quarter turn fasteners (that is, first and second stages  1012 ,  1014 ) allows two panels of varying thicknesses to be assembled together with each other. 
     Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.
The apparatus is a double quarter turn fastener which includes a first element with a head, a square seat, and prongs extending from inwardly adjacent to the sides of the seat outwardly so as to terminate in surfaces with hemispherically extending nubs. The double quarter turn fastener further includes a second element which engages the first element by detent elements or by a rotatable snap fit.