diff --git a/readme.md b/readme.md
index d8fded4..d6c116a 100644
--- a/readme.md
+++ b/readme.md
@@ -2562,7 +2562,7 @@ Filament spool models
 ### Modules
 | Module | Description |
 |:--- |:--- |
-| ```spool(type)``` | Draw specified spool |
+| ```spool(type, filament_depth = 0, filament_colour = "white", filament_d = 3)``` | Draw specified spool with optional filament |
 
 ![spools](tests/png/spools.png)
 
diff --git a/tests/png/spools.png b/tests/png/spools.png
index 9d9847f..2adc977 100644
Binary files a/tests/png/spools.png and b/tests/png/spools.png differ
diff --git a/tests/spools.scad b/tests/spools.scad
index d39c246..7d6ff13 100644
--- a/tests/spools.scad
+++ b/tests/spools.scad
@@ -23,9 +23,9 @@ use <../utils/layout.scad>
 include <../vitamins/spools.scad>
 
 module spools()
-    layout([for(s = spools) spool_height(s)], 100)
+    layout([for(s = spools) spool_height(s)], 100) let(s = spools[$i])
         rotate([90, 0, 90])
-            spool(spools[$i]);
+            spool(s, filament_depth =  spool_depth(s) / 2, filament_colour = [pp1_colour, pp2_colour, pp3_colour, pp4_colour][$i % 4], filament_d = $i ? 3 : 1.75);
 
 if($preview)
     spools();
diff --git a/vitamins/spool.scad b/vitamins/spool.scad
index 56c77e5..19c4c16 100644
--- a/vitamins/spool.scad
+++ b/vitamins/spool.scad
@@ -33,7 +33,7 @@ function spool_hub_taper(type)     = type[8]; //! Diameter at which it tapers do
 function spool_height(type)        = spool_width(type) + 2 * spool_hub_thickness(type); //! Outside width
 function spool_pitch(type)         = spool_width(type) + spool_rim_thickness(type); //! Spacing of the rims
 
-module spool(type, filament_depth = 0, filament_color = "white") { //! Draw specified spool with optional filament
+module spool(type, filament_depth = 0, filament_colour = "white", filament_d = 3) { //! Draw specified spool with optional filament
     vitamin(str("spool(", type[0], "): Filament spool ", spool_diameter(type), " x ", spool_width(type)));
 
     h = spool_height(type);
@@ -59,7 +59,24 @@ module spool(type, filament_depth = 0, filament_color = "white") { //! Draw spec
             [r2, h],
         ]);
 
-    if(filament_depth)
-        color(filament_color)
-            tube(r5 + filament_depth, r5, spool_width(type));
+    if(filament_depth) {
+        w = spool_width(type);
+        r = r5 + filament_depth;
+        color(filament_colour)
+            if(filament_d) {
+                n = round(w / filament_d) + 1;
+                fd = w / n;
+                rotate_extrude($fn = 180) {
+                    for(i = [0 : n -1])
+                        translate([r - fd / 2, i * fd - w / 2 + fd / 2])
+                            circle(d = fd, $fn = 32);
+
+                    translate([r5, -w / 2])
+                        square([filament_depth - fd / 2, w]);
+                }
+            }
+
+            else
+                tube(r, r5, w, $fn = 180);
+    }
 }