diff --git a/attachments.scad b/attachments.scad
index a343d66..d403f85 100644
--- a/attachments.scad
+++ b/attachments.scad
@@ -1649,10 +1649,8 @@ function _find_anchor(anchor, geom) =
             rpts = apply(rot(from=anchor, to=RIGHT) * move(point3d(-cp)), vnf[0]),
             maxx = max(columns(rpts,0)),
             idxs = [for (i = idx(rpts)) if (approx(rpts[i].x, maxx)) i],
-            mm = pointlist_bounds(select(rpts,idxs)),
-            avgy = (mm[0].y+mm[1].y)/2,
-            avgz = (mm[0].z+mm[1].z)/2,
-            mpt = approx(point2d(anchor),[0,0])? [maxx,0,0] : [maxx, avgy, avgz],
+            avep = sum(select(rpts,idxs))/len(idxs),
+            mpt = approx(point2d(anchor),[0,0])? [maxx,0,0] : avep,
             pos = point3d(cp) + rot(from=RIGHT, to=anchor, p=mpt)
         ) [anchor, pos, anchor, oang]
     ) : type == "rect"? ( //size, size2, shift
diff --git a/masks.scad b/masks.scad
index 9f46103..f5d783f 100644
--- a/masks.scad
+++ b/masks.scad
@@ -70,17 +70,11 @@ module chamfer_edge_mask(l=1, chamfer=1, excess=0.1, anchor=CENTER, spin=0, orie
 //       corner_mask(TOP+FWD+RIGHT)
 //           chamfer_corner_mask(chamfer=20);
 //   }
+// Example: Anchors
+//   chamfer_corner_mask(chamfer=20)
+//       show_anchors();
 module chamfer_corner_mask(chamfer=1, anchor=CENTER, spin=0, orient=UP) {
-    pts = 2 * chamfer * [
-        [0,0,1], [1,0,0], [0,1,0], [-1,0,0], [0,-1,0], [0,0,-1]
-    ];
-    faces = [
-        [0,2,1], [0,3,2], [0,4,3], [0,1,4], [5,1,2], [5,2,3], [5,3,4], [5,4,1]
-    ];
-    attachable(anchor,spin,orient, size=[4,4,4]*chamfer) {
-        polyhedron(pts, faces, convexity=2);
-        children();
-    }
+    octahedron(chamfer*4, anchor=anchor, spin=spin, orient=orient) children();
 }
 
 
diff --git a/shapes3d.scad b/shapes3d.scad
index 8d63d63..5437440 100644
--- a/shapes3d.scad
+++ b/shapes3d.scad
@@ -641,6 +641,44 @@ function prismoid(
     ) reorient(anchor,spin,orient, size=[s1.x,s1.y,h], size2=s2, shift=shift, p=vnf);
 
 
+// Function&Module: octahedron()
+// Usage: As Module
+//   octahedron(size, ...);
+// Usage: With Attachments
+//   octahedron(size, ...) { attachments }
+// Usage: As Function
+//   vnf = octahedron(size, ...);
+// Description:
+//   When called as a module, creates an octahedron with axis-aligned points.
+//   When called as a function, creates a [[VNF|vnf.scad]] of an octahedron with axis-aligned points.
+// Arguments:
+//   size = Width of the octahedron, tip to tip.
+//   ---
+//   anchor = Translate so anchor point is at origin (0,0,0).  See [anchor](attachments.scad#anchor).  Default: `CENTER`
+//   spin = Rotate this many degrees around the Z axis after anchor.  See [spin](attachments.scad#spin).  Default: `0`
+//   orient = Vector to rotate top towards, after spin.  See [orient](attachments.scad#orient).  Default: `UP`
+// Example:
+//   octahedron(size=40);
+// Example: Anchors
+//   octahedron(size=40) show_anchors();
+module octahedron(size=1, anchor=CENTER, spin=0, orient=UP) {
+    vnf = octahedron(size=size);
+    attachable(anchor,spin,orient, vnf=vnf, extent=true) {
+        vnf_polyhedron(vnf, convexity=2);
+        children();
+    }
+}
+
+function octahedron(size=1, anchor=CENTER, spin=0, orient=UP) =
+    let(
+        s = size / 2,
+        vnf = [
+            [ [0,0,s], [s,0,0], [0,s,0], [-s,0,0], [0,-s,0], [0,0,-s] ],
+            [ [0,2,1], [0,3,2], [0,4,3], [0,1,4], [5,1,2], [5,2,3], [5,3,4], [5,4,1] ]
+        ]
+    ) reorient(anchor,spin,orient, vnf=vnf, extent=true, p=vnf);
+
+
 // Module: rect_tube()
 // Usage: Typical Rectangular Tubes
 //   rect_tube(h, size, isize, [center], [shift]);