diff --git a/avr/devices/n28/enclosure.scad b/avr/devices/n28/enclosure.scad
index 3861033..a45eeed 100644
--- a/avr/devices/n28/enclosure.scad
+++ b/avr/devices/n28/enclosure.scad
@@ -15,10 +15,15 @@ lid_height = 4;
 lid_tolerance = .3;
 
 hook_height = 1;
-hook_tolerance = .5;
+hook_tolerance = 0.75;
 
 airslit_height = 1.75;
 
+ridge_height = 16;
+ridge_width = 1;
+
+
+
 
 module posts(x, y, z, h, r){
     translate([x, y, z])
@@ -122,11 +127,26 @@ union() {
     translate([(width/2)+0.25, -length/4, height-(hook_height/2)])
       cube([2.5, 7, hook_height], center=true);
 
+    // ridges to hold the pcb
+    translate([(width/2)-wall_thickness, 0, ridge_height/2+(height-ridge_height)])
+      cube([ridge_width, ridge_width, ridge_height], center=true);
+
+    translate([-((width/2)-wall_thickness), 
+               length/8,
+               ridge_height/2+(height-ridge_height)])
+      cube([ridge_width, ridge_width, ridge_height], center=true);
+
+    translate([-((width/2)-wall_thickness), 
+               -length/8,
+               ridge_height/2+(height-ridge_height)])
+      cube([ridge_width, ridge_width, ridge_height], center=true);
+
+
 }
 
 
 /* lid */
-translate([0, 0, 50]) { /* match at Z=17*/
+translate([0, 0, 50]) { /* match at Z=17.5, otherwise 50*/
   difference() {
     union() {
         difference() {