diff --git a/models/pronter_calibration/captive_part.scad b/models/pronter_calibration/captive_part.scad
new file mode 100644
index 0000000..02a6bd5
--- /dev/null
+++ b/models/pronter_calibration/captive_part.scad
@@ -0,0 +1,23 @@
+dia = 15;
+gap = 1;
+height = 10;
+cone_height = 5;
+
+
+module spool(height, dia, cone_height) {
+    cylinder($fn = 120, h = height, d = (dia - 2*cone_height));
+    cylinder($fn = 120, h = cone_height, d1 = dia, d2 = dia - 2*cone_height);
+    translate([0, 0, height - cone_height]) {
+        cylinder($fn = 120, h = cone_height, d1 = dia - 2*cone_height, d2 = dia);
+    }
+}
+
+difference() {
+    translate([-10, -10, 0]) {
+        cube([20, 20, height]);
+    }
+    difference() {
+        spool(height, dia, cone_height);
+        spool(height, dia - gap, cone_height );
+    }
+}
diff --git a/models/pronter_calibration/cube_10_10_10.scad b/models/pronter_calibration/cube_10_10_10.scad
new file mode 100644
index 0000000..45cd3bc
--- /dev/null
+++ b/models/pronter_calibration/cube_10_10_10.scad
@@ -0,0 +1,3 @@
+// a 10mm cube
+
+cube([10, 10, 10]);
\ No newline at end of file
diff --git a/models/pronter_calibration/cube_20_10_20.scad b/models/pronter_calibration/cube_20_10_20.scad
new file mode 100644
index 0000000..6fefa07
--- /dev/null
+++ b/models/pronter_calibration/cube_20_10_20.scad
@@ -0,0 +1,3 @@
+// a 20x10x20mm tall cuboid
+
+cube([20, 10, 20]);
\ No newline at end of file
diff --git a/models/pronter_calibration/cube_20_20_10.scad b/models/pronter_calibration/cube_20_20_10.scad
new file mode 100644
index 0000000..487a8d4
--- /dev/null
+++ b/models/pronter_calibration/cube_20_20_10.scad
@@ -0,0 +1,3 @@
+// a 20x20x10mm tall cuboid
+
+cube([20, 20, 10]);
\ No newline at end of file