referring to fig3 and 4 , a shelf of the present invention includes a pair of rails ( 1 ), spaced apart from one another in a parallel relationship , and vertically mounted on a wall . each of the rails ( 1 ) includes an inner recess ( 111 ) and an outer recess ( 112 ) formed along said rail . the outer recess ( 112 ) has a plurality of positioning holes ( 113 ) formed therealong . the outer recess ( 112 ) is covered by an elongated plate ( 114 ) to enhance its appearance . a rectangular frame ( 2 ) includes a first elongated plate ( 22 ) disposed between the two rails , and a second elongated plate ( 21 ) extending perpendicularly from the first elongated plate ( 22 ). the second elongated plate ( 21 ) has a mounting hole ( 113b ) adjacent to one end thereof . each of an engaging members ( 115 ) have a through - hole ( 113a ) aligned with the mounting hole ( 113b ) of the second elongated plate ( 21 ) and a curved edge . the outer edge of the curved edge has a plurality of notches ( 116 ) along , and the engaging member ( 115 ) is disposed between one end of the elongated plate ( 22 ) and each of the rails ( 1 ). the engaging members ( 115 ) are slidable in the inner recess ( 111 ) of the rail ( 1 ). a hollow tube ( 31 ) has a first end flush with the periphery of the mounting hole ( 113b ) of the second elongated plate ( 21 ). a cap ( 312 ) has a threaded stem and a through - hole ( 313 ) along the axis of the stem . the stem passes through the mounting hole ( 113b ) and holds the hollow tube ( 31 ) in place . a slit ( 212 ) is formed on the second elongated plate ( 21 ) adjacent to said mounting hole ( 113b ). a rod ( 33 ) is received in the hollow tube ( 31 ) around which , a coil spring ( 32 ) is sleeved over the rod ( 33 ). the coil spring ( 32 ) urges a first end of the rod ( 33 ) to extend out of the first end of the hollow tube ( 31 ), passing through the through - hole ( 113a ) of the engaging member ( 115 ), and through the cap ( 312 ) into one of the holes ( 113 ) of the rail . thus , the first elongated plate ( 22 ) is engaged in said rail . a second end of the rod ( 33 ) extends out of the second end of the hollow tube ( 31 ) and is connected to a pull member ( 34 ). under these conditions , the hollow tube ( 31 ) is adjacent to and parallel to the first elongated plate ( 22 ). the second end of the elongated rod ( 33 ) is connected to the pull member ( 34 ) and secured thereat by means of a screw ( 311 ). the first end of the elongated rod ( 33 ) can be retracted from the hole ( 113 ) of the rail ( 1 ) into the hollow tube ( 31 ), by pulling the pull member ( 34 ). thus , the first elongated plate ( 22 ) can be raised or lowered to a desired height along the rails ( 1 ). the second elongated plate ( 21 ) has a slit ( 212 ) adjacent to the mounting hole ( 113b ) of the same . an elongated plate ( 210 ) has a tab ( 214 ) laterally extending from one end thereof . the other end of the elongated plate ( 210 ) has a recess portion ( 215 ) into which recess portion , a serrated plate ( 216 ) is fixedly mounted . the elongated plate ( 210 ) is mounted on the second elongated plate ( 21 ), as illustrated in fig4 with the tab ( 214 ) of the elongated plate extending out of the slit ( 212 ) of the second elongated plate ( 21 ). a toothed rod ( 4 ) has an axial through - hole ( 41 ), into which a first end of a linking rod ( 42 ), is inserted and secured by means of a screw ( 444 ). a threaded wheel ( 43 ) is coaxially mounted in a position adjacent to a second end of the linking rod ( 42 ). the threaded wheel ( 43 ) of the linking rod ( 42 ) is engaged with the serrated end of the elongated plate ( 210 ). the second end of the linking rod ( 42 ) passes through the hole ( 217 ) of the second elongated plate ( 21 ) and is connected to a control arm ( 45 ). a bracket ( 46 ) has a ring ( 47 ) through which the toothed rod ( 4 ) passes . the bracket ( 46 ) is fixed to the other first member ( 22 ), in - between a pair of the second elongated plates ( 21 ). the ring ( 47 ) has an internally toothed hole to engage with the toothed rod ( 4 ). the spring ( 48 ) has one end abutting the inner portion of the bracket ( 46 ) while the other end is fixed in a hole ( 471 ) in the ring ( 47 ). thus the toothed rod 4 is spring loaded , and will return to a predetermined rest condition unless force is applied to rotate it axially . as shown in fig6 the assembly is arranged such that when the toothed rod ( 4 ) is in the rest position , the toothed wheel ( 43 ) holds the plate ( 210 ) in a position where the tab ( 214 ) at the end of the plate ( 210 ) passes through the slit ( 212 ) in the second elongated plate ( 21 ) to engage one of the notches ( 116 ) of the engaging members ( 115 ). the control arm ( 45 ), being fixed to the toothed wheel ( 43 ), can be rotated against the force of the spring ( 46 ) which will cause the wheel ( 43 ) to spin . the teeth of the wheel ( 43 ), being engaged in the serrated plate ( 216 ), will draw the plate ( 210 ) toward the toothed rod ( 4 ), pulling the tab ( 214 ) free of the notch ( 116 ). then the angle of the shelf can be changed . releasing control arm ( 45 ) will allow the assembly to return to the rest condition , fixing the shelf in the selected angular relationship with the rails . as illustrated in fig7 a connecting bar ( 12 ) is provided between the pair of rails ( 1 ). some fastening plates ( 122 , 123 ) are also provided on the connecting bar ( 12 ) through which screws can be inserted to secure the entire assembly to a mounting wall . the method of adjusting the shelf was described above . with the invention thus explained , it is obvious to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the present invention . it is therefore intended that this invention be limited only as indicated in the appended claims .
a shelf has a device to adjust its height on a pair of mounting rails and a device to adjust its angle with respect to the mounting rails .