Just a quick update. The resized prototypes should be here by the weekend. If they fit, the we are 2-3 weeks away from the production versions arriving. If they still don't fit, I'll have to go around the loop again, which will add a further 10 days. The problem is that we are talking fine tolerances on the push-fit. The 3-D printed plastic sample fitted perfectly on a CNC file that specified a 2.5mm gap, but the metal versions, manufactured from the same file, were a sloppy fit. When measured, the 3D printed version was actually 2.25, because there is significant tolerance 3-D printing. I've reduced the gap on the CNC file to 2.5mm, so fingers crossed.