diff --git a/hdd_rack.scad b/hdd_rack.scad
new file mode 100644
index 0000000..d48b2cc
--- /dev/null
+++ b/hdd_rack.scad
@@ -0,0 +1,92 @@
+// Two-way stackable 3.5" HDD rack
+// GPLv3, (c) Vitaliy Filippov, 2018
+
+w = 100;  // HDD width
+h = 29;   // HDD height + spacing
+hl = 147; // HDD length
+l = 25;   // Mount width
+fh = 13;  // Fixer height (must be < h/2)
+t1 = 5;   // Wall thickness
+th = 5;   // Bracket notch thickness
+wo = 6;   // Width offset (must be > 5)
+sw = 5;   // Stack notch thickness
+
+module mount2() {
+    difference() {
+        union() {
+            translate([-t1-wo,-5,-5]) cube(size=[t1,l,5+h]);
+            translate([-t1-wo,-5,-5]) cube(size=[t1*2+w+wo*2,l,5]);
+            translate([w+wo,-5,-5]) cube(size=[t1,l,5+h]);
+            translate([-t1-wo-sw,l-15,-5]) cube(size=[w+wo*2+sw*2+t1*2,5,5]);
+            translate([w,0,0]) cube(size=[wo,5,5]);
+            difference() {
+                translate([-t1-wo-sw,-5,h-5]) cube(size=[sw,l-5,15]);
+                translate([-t1-wo-sw,l-15,h]) cube(size=[sw,l-5,5]);
+            }
+            difference() {
+                translate([w+wo+t1,-5,h-5]) cube(size=[sw,l-5,15]);
+                translate([w+wo+t1,l-15,h]) cube(size=[sw,l-5,5]);
+            }
+            translate([w+wo,-5,h-10]) cube(size=[5+2*sw+2*t1,5,10]);
+            translate([w+wo+2*t1+2*sw,-5,h-10]) cube(size=[5,10,10]);
+        }
+        translate([-t1-wo-1, l-th-10-0.2, h/2-th-0.2]) cube(size=[t1+2,th+0.4,th*2+0.4]);
+        translate([w+wo-1, l-th-10-0.2, h/2-th-0.2]) cube(size=[t1+2,th+0.4,th*2+0.4]);
+        translate([-wo-t1-sw-1,-5-1,h-10]) cube(size=[wo+t1+sw+2,5+1,10]);
+    }
+}
+
+module bracket() {
+    translate([-wo, l-th-10, h/2-th]) cube(size=[5, hl-2*(l-th-10), th*2]);
+    translate([-wo-t1-1, 10, h/2-th]) cube(size=[5+t1+1, th, th*2]);
+    translate([-wo-t1-1, hl-2*(l-th-10)+th, h/2-th]) cube(size=[5+t1+1, th, th*2]);
+}
+
+module fixer() {
+    difference() {
+        union() {
+            translate([w, -5, 0]) cube(size=[wo, l-10, fh]);
+            translate([w-30, -5, 0]) cube(size=[wo+30, 5, fh]);
+        }
+        translate([w-1, 0, -1]) cube(size=[wo+2, 5+0.2, 6+0.2]);
+    }
+}
+
+module cover() {
+    translate([-t1-wo,-5,-5]) cube(size=[t1*2+w+wo*2,l,5]);
+    translate([-t1-wo-sw,l-15,-5]) cube(size=[w+wo*2+sw*2+t1*2,5,5]);
+}
+
+module assembly(c) {
+    color([0.8,0.6,1]) cube(size=[w,hl,27]);
+    color(c) mount2();
+    color(c) translate([0,hl,0]) rotate([0, 0, 180]) mirror() mount2();
+    color([0.5,1,0.5]) {
+        bracket();
+        translate([w,hl,0]) rotate([0, 0, 180]) bracket();
+    }
+    color([0.5,1,1]) {
+        fixer();
+        translate([0,hl,0]) rotate([0, 0, 180]) mirror() fixer();
+    }
+}
+
+module covered_assembly(c) {
+    assembly(c);
+    translate([0, 0, h+5]) {
+        cover();
+        translate([w,hl,0]) rotate([0, 0, 180]) cover();
+    }
+}
+
+translate([0, 0, 0]) assembly();
+translate([0, 0, h+5]) covered_assembly([0.5,0.5,1]);
+translate([-w-2*wo-2*t1-2*sw, 0, 0]) assembly([0.5,0.5,1]);
+translate([-w-2*wo-2*t1-2*sw, 0, h+5]) covered_assembly();
+
+//mount2();
+//fixer();
+//bracket();
+//cover();
+//mirror() mount2();
+//mirror() fixer();
diff --git a/screw_gear.scad b/screw_gear.scad
index 49040b3..5bbbdff 100644
--- a/screw_gear.scad
+++ b/screw_gear.scad
@@ -1,28 +1,43 @@
-screw_gear(8, 4, 2, 8, 18, 32);
+translate([-40, 0, 0]) mirror() rotate([0, 0, 180]) screw_gear(8, 4, 2, 2, 8, 18, 32);
 
-module screw_gear(outer_radius, inner_radius, thickness, thread_length, precision, total_length)
+difference() {
+    union() {
+        for (i=[1:10]) rotate([0, 0, 360*i/10]) screw_gear(8, 6, 2, 60, 64, 18, 64);
+    }
+//    translate([-50, 0, 0]) cube(size=[100,100,100]);
+}    
+#difference() {
+    translate([-15, 0, 0]) mirror() rotate([0, 0, 360/2/10]) {
+        union() {
+            for (i=[1:10]) rotate([0, 0, 360*i/10]) screw_gear(8, 6, 2, 60, 64, 18, 64);
+        }
+    }
+//    translate([-50, 0, 0]) cube(size=[100,100,100]);
+}
+
+module screw_gear(outer_radius, inner_radius, outer_thickness, inner_thickness, thread_length, precision, total_length)
 {
     linear_extrude(height=total_length, twist=360*total_length/thread_length, slices=360)
     polygon(
-        points = screw_crosssection(outer_radius, inner_radius, thickness, thread_length, precision),
-        paths = [ range((precision+8)*2) ]
+        points = screw_crosssection(outer_radius, inner_radius, outer_thickness, inner_thickness, thread_length, precision),
+        paths = [ range((precision+precision)*2) ]
     );
 }
 
-function screw_crosssection(outer_radius, inner_radius, thickness, thread_length, precision) =
+function screw_crosssection(outer_radius, inner_radius, outer_thickness, inner_thickness, thread_length, precision) =
     concat(
-        [ for (x=[1 : 8]) polar(outer_radius, thickness*360/thread_length*x/8) ],
+        [ for (x=[1 : precision]) polar(outer_radius, 360*outer_thickness/thread_length*x/precision - outer_thickness/2/thread_length*360) ],
         [ for (x=[1 : precision])
             polar(
                 outer_radius-(outer_radius-inner_radius)*x/precision,
-                thickness*360/thread_length + x/precision*(180-(thickness*360/thread_length))
+                outer_thickness/2/thread_length*360 + 360*(1-outer_thickness/thread_length-inner_thickness/thread_length)/2*x/precision
             )
         ],
-        [ for (x=[1 : 8]) polar(inner_radius, 180 + thickness*360/thread_length*x/8) ],
+        [ for (x=[1 : precision]) polar(inner_radius, 180 + 360*inner_thickness/thread_length*x/precision - inner_thickness/2/thread_length*360) ],
         [ for (x=[1 : precision])
             polar(
                 inner_radius+(outer_radius-inner_radius)*x/precision,
-                180 + thickness*360/thread_length + x/precision*(180-(thickness*360/thread_length))
+                180 + inner_thickness/2/thread_length*360 + 360*(1-outer_thickness/thread_length-inner_thickness/thread_length)/2*x/precision
             )
         ]
     );