Possible end-cap design; not sure how well this one will work.

endcap-flat.scad

@@ -0,0 +1,56 @@
+CYLINDER_DIAMETER = 40;
+CYLINDER_THICKNESS = 4;
+
+ENDCAP_THICKNESS = 2;
+ENDCAP_LENGTH = 4;
+
+TOLERANCE = 0.7;
+//DETAIL = 20;
+DETAIL = 100;
+
+module endcap()
+{
+    union()
+    {
+        cylinder(r = CYLINDER_DIAMETER / 2, h = ENDCAP_THICKNESS, $fn = DETAIL);
+        cylinder(r = CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE, h = ENDCAP_LENGTH, $fn = DETAIL);
+    }
+}
+
+module clip_style_1()
+{
+    intersection()
+    {
+        translate(v = [CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE, 2.5, ENDCAP_LENGTH])
+            rotate(a = [90, 0, 0])
+                linear_extrude(height = 5, center = false, convexity = 3, twist = 0, slices = DETAIL)
+                    polygon(points=[[0,0],[-5, 0],[0, 10]]);
+        cylinder(r = CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE, h = 20, $fn = DETAIL);
+    }
+    translate(v = [CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE - 0.25, 0, 12])
+        sphere(r = 0.5, $fn = DETAIL);
+    translate(v = [CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE - 0.25, 1.5, 12])
+        sphere(r = 0.5, $fn = DETAIL);
+    translate(v = [CYLINDER_DIAMETER / 2 - CYLINDER_THICKNESS - TOLERANCE - 0.25, -1.5, 12])
+        sphere(r = 0.5, $fn = DETAIL);
+}
+
+module clip()
+{
+    clip_style_1();
+}
+
+module clips()
+{
+    for (angle = [0 : 120 : 240])
+    {
+        rotate(a = [0, 0, angle])
+            clip();
+    }
+}
+
+union()
+{
+    endcap();
+    clips();
+}