diff --git a/libtest.png b/libtest.png
index c441cca..9292213 100644
Binary files a/libtest.png and b/libtest.png differ
diff --git a/libtest.scad b/libtest.scad
index f591b61..5efe5f5 100644
--- a/libtest.scad
+++ b/libtest.scad
@@ -482,7 +482,7 @@ cable_strip_y = sheets_y + 30;
 translate([0, transformers_y])
     servo_motors();
 
-translate([x4 + 200, belts_y + 58]) {
+translate([x4 + 200 + 16, belts_y + 58]) {
     belt_test();
 
     translate([0, 60])
diff --git a/readme.md b/readme.md
index 01b8a60..820523a 100644
--- a/readme.md
+++ b/readme.md
@@ -437,10 +437,14 @@ Individual teeth are not drawn, instead they are represented by a lighter colour
 ### Vitamins
 | Qty | Module call | BOM entry |
 | ---:|:--- |:---|
+|   1 | `belt(GT2x12, [ ... ])` |  Belt GT2 x 12mm x 128mm |
 |   1 | `belt(GT2x6, [ ... ])` |  Belt GT2 x 6mm x 128mm |
-|   1 | `belt(GT2x6, [ ... ])` |  Belt GT2 x 6mm x 552mm |
-|   2 | `belt(GT2x6, [ ... ])` |  Belt GT2 x 6mm x 556mm |
+|   1 | `belt(GT2x6, [ ... ])` |  Belt GT2 x 6mm x 584mm |
+|   2 | `belt(GT2x6, [ ... ])` |  Belt GT2 x 6mm x 588mm |
 |   1 | `belt(GT2x9, [ ... ])` |  Belt GT2 x 9mm x 128mm |
+|   1 | `belt(GT3x12, [ ... ])` |  Belt GT3 x 12mm x 128mm |
+|   1 | `belt(GT3x6, [ ... ])` |  Belt GT3 x 6mm x 128mm |
+|   1 | `belt(GT3x9, [ ... ])` |  Belt GT3 x 9mm x 128mm |
 |   1 | `belt(T2p5x6, [ ... ])` |  Belt T2.5 x 6mm x 130mm |
 |   1 | `belt(T5x10, [ ... ])` |  Belt T5 x 10mm x 130mm |
 |   1 | `belt(T5x6, [ ... ])` |  Belt T5 x 6mm x 130mm |
diff --git a/tests/belts.scad b/tests/belts.scad
index cc47183..01ffe81 100644
--- a/tests/belts.scad
+++ b/tests/belts.scad
@@ -21,14 +21,20 @@ include <../core.scad>
 include <../vitamins/pulleys.scad>
 use <../vitamins/insert.scad>
 use <../utils/layout.scad>
+use <../utils/maths.scad>
 
 module belt_test() {
-    p2 = [-75, -50];
-    p3 = [-75, 100];
-    p4 = [ 75, 100];
+    widths = [for(b = belts) belt_width(b)];
+    gap = 5;
+    belts_width = sumv(widths) + (len(belts) - 1) * gap;
+    width = belts_width + 50;
 
-    p5 = [ 75 + pulley_pr(GT2x20ob_pulley) - pulley_pr(GT2x16_plain_idler), +pulley_pr(GT2x16_plain_idler)];
-    p6 = [-75 + pulley_pr(GT2x20ob_pulley) + pulley_pr(GT2x16_plain_idler), -pulley_pr(GT2x16_plain_idler)];
+    p2 = [-width / 2, -50];
+    p3 = [-width / 2, 100];
+    p4 = [ width / 2, 100];
+
+    p5 = [ width / 2 + pulley_pr(GT2x20ob_pulley) - pulley_pr(GT2x16_plain_idler), +pulley_pr(GT2x16_plain_idler)];
+    p6 = [-width / 2 + pulley_pr(GT2x20ob_pulley) + pulley_pr(GT2x16_plain_idler), -pulley_pr(GT2x16_plain_idler)];
 
     module pulleys(flip = false) {
         translate(p2) rotate([0, flip ? 180 : 0, 0]) pulley_assembly(GT2x20ob_pulley);
@@ -70,15 +76,15 @@ module belt_test() {
             pulleys(flip=true);
         }
 
-    translate([-25, 0, 10])
-        layout([for(b = belts) belt_width(b)], 10)
+    translate([-belts_width / 2, 0, 10])
+        layout(widths, gap)
             rotate([0, 90, 0])
                 belt(belts[$i], [[0, 0, 20], [0, 1, 20]], belt_colour = $i%2==0 ? grey(90) : grey(20), tooth_colour = $i%2==0 ? grey(70) : grey(50));
 
     // new example with open loop - this is a simplified example of the style used for example for the BLV 3D printer
     pulley = GT2x20ob_pulley;
     idler = GT2x16_plain_idler;
-    corners = [[-75,-50],[75,100]];
+    corners = [[-width / 2,-50],[width / 2,100]];
     carriagepos = [0,0];
     carriagew = 80;
 
@@ -94,7 +100,7 @@ module belt_test() {
     translate_z(-30) {
         belt(belt, points, open=true, auto_twist=true);
         for (p = points)
-            if (is_list(p.z))
+            if(is_list(p.z))
                 translate([p.x, p.y, 0])
                     pulley_assembly(p.z);
     }
diff --git a/tests/png/belts.png b/tests/png/belts.png
index ae471be..d39b4b6 100644
Binary files a/tests/png/belts.png and b/tests/png/belts.png differ
diff --git a/vitamins/belts.scad b/vitamins/belts.scad
index 96a3fef..cf4f5e6 100644
--- a/vitamins/belts.scad
+++ b/vitamins/belts.scad
@@ -20,17 +20,23 @@
 //
 // Belt model
 //
-//                p     w  t     t     p
-//                i     i  h     o     i
-//                t     d  i     o     t
-//                c     t  c     t     c
-//                h     h  k     h     h line from tooth base
+//               p     w  t     t     p
+//               i     i  h     o     i
+//               t     d  i     o     t
+//               c     t  c     t     c
+//               h     h  k     h     h line from tooth base
 //
-T5x6 =  ["T5",    5,    6, 2.2,  1.2,  0.5];
-T5x10 = ["T5",    5,   10, 2.2,  1.2,  0.5];
-T2p5x6 =["T2.5",  2.5,  6, 1.7,  0.7,  0.3];
-GT2x6 = ["GT2",   2.0,  6, 1.38, 0.75, 0.254];
-GT2x9 = ["GT2",   2.0,  9, 1.38, 0.75, 0.254];
+T5x6 =  ["T5",     5,  6, 2.2,  1.2,  0.5];
+T5x10 = ["T5",     5,  10,2.2,  1.2,  0.5];
+T2p5x6 =["T2.5", 2.5,  6, 1.7,  0.7,  0.3];
 
-belts = [T5x6, T5x10, T2p5x6, GT2x6, GT2x9];
+GT2x6 = ["GT2",  2.0,  6, 1.38, 0.75, 0.254];
+GT2x9 = ["GT2",  2.0,  9, 1.38, 0.75, 0.254];
+GT2x12 =["GT2",  2.0, 12, 1.38, 0.75, 0.254];
+
+GT3x6 = ["GT3",  2.0,  6, 1.52, 0.75, 0.254];
+GT3x9 = ["GT3",  2.0,  9, 1.52, 0.75, 0.254];
+GT3x12 =["GT3",  2.0, 12, 1.52, 0.75, 0.254];
+
+belts = [T5x6, T5x10, T2p5x6, GT2x6, GT2x9, GT2x12, GT3x6, GT3x9, GT3x12];
 use <belt.scad>