referring in detail to the drawings , the article display unit 2 of fig1 comprises panels 4 with vertical slots 6 , a panel 8 with horizontal slots 10 and a panel 12 with diagonal slots 14 . the article display unit 16 of fig2 comprises panels 18 , 20 , 22 , 24 , 26 , 28 , 30 and 32 all containing diagonal slots 14 . the unit 16 also comprises the cornice 34 , a base platform 36 and hinge means ( not shown ) for the panel 22 . the panels of the units 2 and 16 are formed of special panel members provided by the invention as described in more detail below . the major areas of display units of the invention , e . g ., units 2 & amp ; 16 , are formed of inside panel members of two types that are basically the same , namely , panel members 40a used to form free - standing display units 42 ( fig4 & amp ; 6 ) and panel members 40b used to form wall - mounted display units 44 ( fig5 & amp ; 8 ). a second type of panel members of the invention are the end type , namely , panel members 46a & amp ; 47 for the ends of free - standing units such as unit 42 and end panel members 46b & amp ; 47 for the ends of wall - mounted units such as unit 44 . the member 46b is identical to member 46a except for the screw holes s . a third type of panel member of the invention is the corner type , namely , panel members 48a for the corners of free - standing units such as unit 42 and corner panel members 48b for corners of wall - mounted units such as unit 44 . members 48b are identical to members 48a except for screw holes s . regardless of whether a panel member is an inside type , corner type or end type , they all are formed of certain basic elements . with reference to panel member 40a ( fig6 & amp ; 10 ), it comprises a first rectangular web 50 having a length substantially greater than its width , a second rectangular web 52 having a length equal to the length of web 50 and a width less than that length and a third web 54 integral with webs 50 & amp ; 52 and perpendicular thereto fixing the webs 50 & amp ; 52 in spaced apart , parallel position . the member 50a further comprises an integral leg element 56 extending laterally from web 50 in the direction of web 52 and an integral lug element 58 extending laterally from web 52 in the direction of web 50 . the leg element 56 is structured to interlock with a lug element 58 of an adjacent panel member , e . g ., the corner member 48a . the leg elements 56 and lug elements 58 are preferrably l - shaped , i . e ., the leg elements 56 are formed of a base element 56a and a lateral element 56b and the lug elements also have a base element 58a and lateral element 58b . the base element 56a &# 39 ; ( see fig4 & amp ; 5 ) may be tapered to assist in the interlocking of the leg elements 56 with lug elements 58 . the leg elements 56 extend a greater distance from the webs 50 than the lug elements 58 extend from the webs 52 . the longitudinal edges 60 & amp ; 60 &# 39 ; of the webs 50 are preferrably c - shaped as are the longitudinal edges 62 & amp ; 62 &# 39 ; of webs 52 . the inside panel members 40b differ from the inside panel members 40a because they include screw holes h and the longitudinal edges 63 and 63 &# 39 ; are less extended from the elements 54 and 58 than are the edges 62 and 62 &# 39 ;. actually , the members 40a and 40b could be identical , but the difference in the edges 63 & amp ; 63 &# 39 ; vs . 62 & amp ; 62 &# 39 ; save metal or other material from which the members 40b are constructed . the leg elements 56 are set back from the respective longitudinal edges 60 of webs 50 an appreciable distance as are lug elements 58 from the longitudinal edges 62 of webs 52 so that when a leg element 56 is interlocked with a lug element 58 of another panel member , e . g ., member 48a , slots 64 are formed between the adjacent panel members . these slots may be , in a final display unit 2 , vertical slots 6 , horizontal slots 10 or diagonal slots 14 . with the inside panel members 40a , the webs 50 are equal in width to the webs 52 and the web 54 connects to web 52 back away from the longitudinal edge 62 &# 39 ;. with the inside panel members 40b , the web 50 is wider than the web 52a in order to save construction material as aforesaid . with the end panel members 47 , the webs 50b are wider than the webs 52b and the third web 54a connects to webs 50b and 52b along their longitudinal sides 60 &# 39 ; a and 62a respectively . the longitudinal sides 60a and 62 &# 39 ; a of webs 50b and 52b respectively are c - shaped . the member has a leg element 56 , does not include a lug element , but does have a channel element 65 integral with web 54a . the end panel members 46a & amp ; 46b include a lug element 58 , but no leg element . also the first web 50b is narrower than the second web 52 . a fourth web 70 extends laterally from the longitudinal edge 60 &# 39 ; a of web 50b and joins the longitudinal edge 72 of the l - shaped member 74 . a channel 65 is formed integral with the web 70 . in the corner panel members 48a and 48b , the first web comprises a first flat portion 50c and a second flat portion 50d normal to portion 50c . the third web 54 extends from the portion 50c and the leg element 56 extends from portion 50d . the second web 52b is fixed apart and parallel to the portion 50c by the web 54 . there is also a y - shaped element 66 that extends from the first web at the joint of the first flat portion 50c with the second flat portion 50d at an angle of approximately 45 ° relative to both flat portions . the free ends 68 of y - element 66 are preferrably c - shaped , as are the longitudinal edges 60 and 60 &# 39 ; of the first web flat portions 50d and 50c respectively . to assemble a wall - mounted display unit such as unit 44 , an s - shaped clip 76 ( see fig8 a ) is fixed to a wall ( not shown ) by a screw 78 and an end member 46b is slipped under the clip 76 as shown in fig8 . a second screw 78 is next screwed through the hole s of the member 46b and then the leg element 56 of an inside member 40b is locked into the lug element 58 of the member 46b . a screw is screwed through the hole s of member 40b and then the leg element 56 of the corner member 48b is locked into the lug element 58 of member 40b . next a screw is screwed through hole s of corner member 48b and the leg element 56 of member 40b is locked into the lug element 58 of member 48b . finally , a screw is screwed through the hole s of member 40b , a z - shaped clip 80 is screwed to the wall ( not shown ) a measured distance from the edge 63 of member 40b and end member 47 is slipped under the clip 80 and the leg element 56 of member 47 is locked into the lug element 58 of member 40b . this completes the wall mounting of the display unit 44 in which the heads of the screws 78 are substantially hidden from view . display units of most any desired size may be assembled and wall mounted using the stepwise procedure as described . the assembly of free - standing and wall - mounted display units from the new panel members of the invention is further illustrated by fig3 - 5 and 15 - 17 . in order to finish or close - off the transverse edges of display units , cap strips are used . fig5 shows a wall - mounted unit 44a ( without mounting screws installed ) comprising panel member 47 with its transverse edge 82 , member 40b with its transverse edge 84 and member 46b with its transverse edge 86 . holes h are punched or drilled in the members 47 , 40b and 46b near the transverse edges and slots 88 are cut in the ends of the webs 54 and leg elements 56 present in the assembly to a depth at least as deep as the length of the leg 90 of the t - shaped end cap 92 . holes 94 are preformed in the leg 90 to correspond to the spacing of holes h and the transverse edges 96 of the leg 90 are cut back the width of the webs 54a and 70 ( see fig1 ). as a result , the end cap 92 can be inserted in the direction of the arrow in fig4 into the end of the unit 44a to provide a closed or finished appearance . the cap 92 can be held in place by self - tapping screws 96 or other fasteners as shown in the horizontally positioned cap 92 in fig3 . the free - standing display unit 42a of fig4 is assembled from panel members 47 , 40a and 46a and closed with an end cap 92 in the same manner described above for unit 44a . fig1 illustrates the assembly of a free - standing display unit 42b with vertical slots 62 and end caps 92 in the horizontal position . fig1 - 23 illustrate various ways in which the outside surfaces of panel members of the invention are structured . by way of example , fig1 - 23 show inside panel members for wall - mounted units , e . g ., member 40b in fig2 is identical to member 40b in fig8 but the surface structuring can be applied to any of the other panel members 40a , 46a , 46b , 47 , 48a and 48b . in fig1 , the panel member 40c has a convex surface portion 98 . in fig1 , the panel member 40d has a concave surface portion 100 . in fig2 , the panel member 40e has an indent surface portion 102 and in fig2 , the panel member 40f has a slightly bowed surface 104 . the panel member 40g in fig2 illustrates a further surface modification , i . e ., it has side grooves 106 in the web 50b into which surface strips 108 may be inserted and held . such strips can be plastic , metal , paper or other rigid or simi - rigid material of any desired color , surface finish , etc . as previously indicated , the new article display units provide parallel slots into which various forms of clips , hooks or other mounting devices may be inserted and held for supporting , directly or indirectly , any desired article . some preferred forms of accessory clips of the invention are illustrated in fig2 - 34 . the free - standing display unit 42 has a single bracket accessory clip 110 mounted on surface 112 and a double bracket accessory clip 114 mounted on surface 116 . elongated electric light tubes l may be included in the display units to provide additional dramatic effects . the accessory clip 110 comprises a bolt 118 , nut 120 , clamp 122 and single opening bracket 124 . the bolt 118 has a knurled head 126 with hex wrench recess 128 . the nut 120 comprises threaded ring portion 130 , wing portion 132 and ledge portion 134 . the clamp 122 comprises rear face section 136 , front face section 138 , holes 140 and arcuate portion 142 . the free ends 144 of bracket 124 slip into the arcuate portion 142 of clamp 122 , bolt 118 in partly threaded into nut 120 , this , in turn , is inserted into the slot 64 ( in the position shown in broken line in fig2 ), twisted to bridge slot 64 with wing portion 132 ( see fig2 ) and the bolt is then tightened to close the clamp 122 about the bracket ends 144 ( see fig2 ). the double bracket clip 114 is similar to clip 122 , but has two clamp portions 142 and 142a in which two brackets 124 and 124a are held . fig2 - 30 illustrate how the accessory clips 110 and 114 may be mounted in horizontal slots 10 , diagonal slots 14 and vertical slots 6 . in addition to closing the exposed ends of display units with end slips 92 , other closure devices may be used as shown in fig3 and 36 . thus , the circular display unit 145 with vertical slots 6 comprises a base disc plate 148 and top disc plate 150 and the cubic display unit 152 with vertical slots 6 comprises a square base plate 154 and a square top plate 156 . fig3 - 39 illustrate how free - standing display units may be varied in slot positioning , e . g ., unit 158 has vertical slots 6 , unit 160 has diagonal slots 14 and unit 162 has horizontal slots 10 . these units have triangular feet elements 164 to hold them in an upright position .