diff --git a/utils/thread.scad b/utils/thread.scad
index caa974f..da7ea76 100644
--- a/utils/thread.scad
+++ b/utils/thread.scad
@@ -47,7 +47,7 @@ thread_colour_factor = 0.8; // 60 degree threads appear too bright due to the an
 
 function thread_profile(h, crest, angle, overlap = 0.1) = //! Create thread profile path
     let(base = crest + 2 * (h + overlap) * tan(angle / 2))
-        [[-base / 2, -overlap, 0], [-crest / 2, h, 0], [crest / 2, h, 0], [base / 2, -overlap, 0]];
+        [[-base / 2, -overlap, 0], [-crest / 2, h, 0], if(crest) [crest / 2, h, 0], [base / 2, -overlap, 0]];
 
 module thread(dia, pitch, length, profile, center = true, top = -1, bot = -1, starts = 1, solid = true, female = false, colour = undef) { //! Create male or female thread, ends can be tapered, chamfered or square
     assert(is_undef(colour) || is_list(colour), "Thread colour must be in [r, g, b] form");
diff --git a/vitamins/insert.scad b/vitamins/insert.scad
index b1a784a..9bfa984 100644
--- a/vitamins/insert.scad
+++ b/vitamins/insert.scad
@@ -212,13 +212,10 @@ module threaded_insert(type) { //! Draw specified threaded insert, for use in wo
 
     thread_l = insert_length(type) - z; // - insert_ring1_h(type);
 
-
-
-
     vitamin(str("threaded_insert(", type[0], "): Threaded insert M", insert_screw_diameter(type), " x ", length, "mm"));
     union() {
         color(silver)
-            difference() {
+            render() difference() {
                 base_insert(type);
                 translate_z(-socket/2 + 0.01)
                     cylinder(r=socket, $fn = 6, h=socket/2);
@@ -245,5 +242,4 @@ module threaded_insert(type) { //! Draw specified threaded insert, for use in wo
                 female = false,
                 colour = silver);
     }
-
 }