diff --git a/rack/back_wall.scad b/rack/back_wall.scad
new file mode 100644
index 0000000..33c9c7d
--- /dev/null
+++ b/rack/back_wall.scad
@@ -0,0 +1,45 @@
+include <config.scad>
+
+module back_wall(size, margin, screw_hole, thickness) {
+     total_size = size + [0, margin[0] + margin[1]];
+     feet_size = 5;
+     padding = 0.2*feet_size;
+     color("Lime", .5)
+          linear_extrude(thickness)
+          difference() {
+          union() {
+               square(total_size);
+               translate([total_size[0]/2, padding, 0])
+                    circle(r=feet_size, $fn=circle_res);
+
+               translate([0, margin[1]/2-thickness, 0]) {
+                    translate([-thickness, 0, 0]) square(thickness);
+                    translate([total_size[0] , 0, 0]) square(thickness);
+               }
+               translate([0, margin[1] + size[1], 0]) {
+                    translate([-thickness, 0, 0]) square(thickness);
+                    translate([total_size[0] , 0, 0]) square(thickness);
+               }
+
+          }
+
+          translate([size[0]/2, screw_hole/2, 0]) {
+               translate([0, margin[1]/2-thickness, 0]) {
+                    translate([-size[0]/6, 0, 0]) circle(d=screw_hole, $fn = circle_res);
+                    translate([ size[0]/6, 0, 0]) circle(d=screw_hole, $fn = circle_res);
+               }
+
+               translate([0, margin[1] + size[1], 0]) {
+                    translate([-size[0]/6, 0, 0]) circle(d=screw_hole, $fn = circle_res);
+                    translate([ size[0]/6, 0, 0]) circle(d=screw_hole, $fn = circle_res);
+               }
+          }
+
+          translate([total_size[0]/2, total_size[1]+padding, 0])
+               circle(r=feet_size, $fn=circle_res);
+
+     }
+}
+
+
+back_wall([pcb_support[0] + safe_padding * 2, nb_nodes * node_clearance], sides_margin, m3, pvc_thickness);
diff --git a/rack/config.scad b/rack/config.scad
index 9c83815..acc2127 100644
--- a/rack/config.scad
+++ b/rack/config.scad
@@ -1,23 +1,24 @@
 nb_nodes = 2;
 node_clearance =30;
 
 m3 = 3 + 0.5;
+m3_length = 10;
 pvc_thickness = 3;
 pcb_hole_spacing = [49,  58];
 pcb_support_x_margin = 10;
 pcb_support_y_margin = [5,  23];
 pcb_support = pcb_hole_spacing + [pcb_support_x_margin*2,
                                   pcb_support_y_margin[0] + pcb_support_y_margin[1]];
 
 safe_padding = 1;
 rail_pad = [pvc_thickness, 10];
 notch = rail_pad + [1, 1];
 pad = [pvc_thickness, 5];
 
 sides_margin = [8, 15];
 
 pcb_delta = 10;
 side_length = pcb_support[1] + pcb_delta * 2;
 rail_size = [5, side_length];
 
 circle_res = 25;
\ No newline at end of file
diff --git a/rack/nut_fix.scad b/rack/nut_fix.scad
index e786021..4417d03 100644
--- a/rack/nut_fix.scad
+++ b/rack/nut_fix.scad
@@ -1,15 +1,16 @@
-module nut_fix_m3() {
+include <config.scad>
+module nut_fix_m3(length, thickness) {
 //http://www.farnell.com/datasheets/1661818.pdf
      padding = .2;
      m3 = 3;
      nut = [2.4, 5.5];
      nut_h = nut + [padding, padding];
      m3_h = m3 + padding;
-     depth = [5, 2];
+     safety = 2;
+     total_depth = length - thickness + safety;
      union() {
-          translate([0, -m3_h/2, 0]) square([depth[0] + depth[1] + nut_h[0], m3_h]);
-          translate([depth[0], -nut_h[1]/2, 0]) square(nut_h);
+          translate([0, -m3_h/2, 0]) square([total_depth, m3_h]);
+          translate([total_depth - nut_h[0] - safety, -nut_h[1]/2, 0]) square(nut_h);
      }
 }
 
-nut_fix_m3();
diff --git a/rack/rack.scad b/rack/rack.scad
index ff286fe..41de8a8 100644
--- a/rack/rack.scad
+++ b/rack/rack.scad
@@ -1,50 +1,57 @@
 include <config.scad>;
-use <odroid.scad>;
 
+use <odroid.scad>;
 use <pcb_support.scad>;
 use <side_wall.scad>;
 use <top_bottom_wall.scad>;
 use <rails.scad>;
+use <back_wall.scad>;
 
 translate ([0, -pcb_delta, 0]) {
-translate([-(pcb_support[0]/2 + safe_padding), ,0]) {
-     rotate([0,-90,0]) side_wall(nb_nodes, node_clearance,
-                                 side_length, sides_margin, notch,
-                                 pvc_thickness, m3, safe_padding);
+     translate([-(pcb_support[0]/2 + safe_padding), ,0]) {
+          rotate([0,-90,0]) side_wall(nb_nodes, node_clearance,
+                                      side_length, sides_margin, notch,
+                                      pvc_thickness, m3, safe_padding);
 
-     translate([0,pvc_thickness, -sides_margin[1]/2-pvc_thickness])
-          top_bottom_wall([pcb_support[0] + safe_padding * 2, side_length], pad, 3);
+          translate([0,pvc_thickness, -sides_margin[1]/2-pvc_thickness])
+               top_bottom_wall([pcb_support[0] + safe_padding * 2, side_length], pad, pvc_thickness, m3_length);
 
-     translate([0,pvc_thickness, node_clearance * nb_nodes])
-          top_bottom_wall([pcb_support[0] + safe_padding * 2, side_length], pad, 3);
+          translate([0,pvc_thickness, node_clearance * nb_nodes])
+               top_bottom_wall([pcb_support[0] + safe_padding * 2, side_length], pad, pvc_thickness, m3_length);
+
+          translate([0,side_length, -sides_margin[1]]) rotate([90,0,0])
+               back_wall([pcb_support[0] + safe_padding * 2, nb_nodes * node_clearance], sides_margin, m3, pvc_thickness);
+     }
+
+     translate([pcb_support[0]/2 + safe_padding + pvc_thickness, 0,0]) rotate([0,-90,0])
+          side_wall(nb_nodes, node_clearance,
+                    side_length, sides_margin, notch,
+                    pvc_thickness, m3, safe_padding);
 
-}
 
-translate([pcb_support[0]/2 + safe_padding + pvc_thickness, 0,0]) rotate([0,-90,0])
-side_wall(nb_nodes, node_clearance,
-          side_length, sides_margin, notch,
-          pvc_thickness, m3, safe_padding);
 }
 
+
+
 for(p = [1:nb_nodes]) {
      z = (p-1)*node_clearance;
      translate([-pcb_support[0]/2,0,z])
           pcb_support(p, pcb_hole_spacing,
                       pcb_support_x_margin, pcb_support_y_margin,
                       pvc_thickness, 3);
 
      translate([-58/2,-2,pvc_thickness+z]) odroid();
 
 
      translate([0, - pcb_delta + pvc_thickness, z - pvc_thickness]) {
           translate([-pcb_support[0]/2 - safe_padding, 0, 0]) {
                translate([0,0,pvc_thickness * 2 + safe_padding]) rail_top(rail_size, rail_pad, pvc_thickness);
                rail_bottom(rail_size, rail_pad, pvc_thickness);
           }
           translate([pcb_support[0]/2 + safe_padding,0,0]) {
                translate([0,0,pvc_thickness * 2 + safe_padding]) mirror([1,0,0]) rail_top(rail_size, rail_pad, pvc_thickness);
                mirror([1,0,0]) rail_bottom(rail_size, rail_pad, pvc_thickness);
           }
      }
 
 }
diff --git a/rack/top_bottom_wall.scad b/rack/top_bottom_wall.scad
new file mode 100644
index 0000000..25832b2
--- /dev/null
+++ b/rack/top_bottom_wall.scad
@@ -0,0 +1,41 @@
+use <nut_fix.scad>;
+module top_bottom_wall(side_size, pad, thickness, m3_length) {
+     size = side_size - [0, thickness*2];
+     color("MediumAquamarine", .5)
+          translate([0,-thickness,0])
+          linear_extrude(thickness)
+          difference () {
+          translate([0, thickness, 0])
+               union() {
+               square(size);
+               translate([-pad[0],0 , 0]) {
+                    translate([0, 0,0]) square(pad);
+                    translate([0,size[1]-pad[1],0]) square(pad);
+               }
+               translate([size[0],0 , 0]) {
+                    translate([0, 0,0]) square(pad);
+                    translate([0,size[1]-pad[1],0]) square(pad);
+               }
+          }
+
+          translate([0, side_size[1]/2, 0]) {
+               translate([0, -side_size[1]/6, 0]) nut_fix_m3(m3_length, thickness);
+               translate([0,  side_size[1]/6, 0]) nut_fix_m3(m3_length, thickness);
+          }
+          translate([size[0], side_size[1]/2, 0]) {
+               mirror([1,0,0]) {
+                    translate([0, -side_size[1]/6, 0]) nut_fix_m3(m3_length, thickness);
+                    translate([0,  side_size[1]/6, 0]) nut_fix_m3(m3_length, thickness);
+               }
+          }
+
+          translate([size[0]/2, size[1]+thickness, 0]) {
+               translate([-size[0]/6, 0, 0]) rotate([0,0,-90]) nut_fix_m3(m3_length, thickness);
+               translate([ size[0]/6, 0, 0]) rotate([0,0,-90]) nut_fix_m3(m3_length, thickness);
+          }
+
+     }
+}
+
+include <congig.h>
+top_bottom_wall([pcb_support[0] + safe_padding * 2, side_length], pad, pvc_thickness, m3_length);