diff --git a/render/form3_test.go b/render/form3_test.go
index d668622..5361283 100644
--- a/render/form3_test.go
+++ b/render/form3_test.go
@@ -54,6 +54,12 @@ func TestForm3Gen(t *testing.T) {
 		view     viewConfig
 		formFunc func(t testing.TB, stlpath string)
 	}{
+		{
+			name:     "knurl ",
+			defacto:  "testdata/defactoKnurl.png",
+			formFunc: knurlToSTL,
+			view:     defaultView,
+		},
 		{
 			name:     "bolt",
 			defacto:  "testdata/defactoBolt.png",
@@ -125,6 +131,14 @@ func hexToSTL(t testing.TB, filename string) {
 	}
 }
 
+func knurlToSTL(t testing.TB, filename string) {
+	object, _ := thread.KnurledHead(.5, 1, .1)
+	err := render.CreateSTL(filename, render.NewOctreeRenderer(object, quality))
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 func boltToSTL(t testing.TB, filename string) {
 	object, err := thread.Bolt(thread.BoltParms{
 		Thread:      thread.ISO{D: 16, P: 2}, // M16x2
diff --git a/render/testdata/defactoKnurl.png b/render/testdata/defactoKnurl.png
new file mode 100644
index 0000000..435c163
Binary files /dev/null and b/render/testdata/defactoKnurl.png differ