The old old old style of reeds were tiny copper crosses. In the 1960's Cox started shipping out a rectangle with rounded ends. Cox has always shipped their reeds made out of spring steel. The patent for the rectangle shaped reeds was originally done for teflon. This made it fine for Cox to make their reeds out of steel. That is why Cox does not make their reeds out of teflon. Cox does not own the patent for the teflon reeds. Many people have tried to make reeds out of many things. Teflon in several thicknesses and shapes steel several thicknesses and shapes, copper again same thing, polyethlyene, brass, PVC, Their are only a very few of these items and combinations that even work. Many of them do not even work in any fashion. a Teflon cross in any thickness. A spring steel cross will work but the rpm ranges are much lower than normal, PVC crosses do not work any thickness. PVC in a rounded rectangle will work at reduced speed and not for very long as the PVC will crack after a short life span. Copper work hardens as a rectangle and a cross after a short time. To restore a copper or brass cross to original soft state first clean the items with abrasive copper cleaner. Brasso comet even fine grade sand paper 1500 to 2000 grit wet&dry. do both sides. Then using an acetylene torch  you blacken the whole cross while holding it with hemostat by edges. Then you  need to heat the cross until the cross gets hot enough to remove the  black soot deposit on it. This will cause the copper to be annealed to a soft state. you will need to do this every 2 hrs run time.  The steel you will have to throw away as it does not take a good anneal process. So we are left with one choice if you want maximum RPM I have gotten 20000+ RPM using Teflon Rectangles with a 7X4 MasterScrew Prop and a muffler on a 049 baby bee old style crankcase. Using only 25% nitro. I have gotten higher speeds but I do not have the photos to prove it so we will leave it a 20K + RPM There are only Two place to purchase the Teflon Rounded Rectangle. Davis Diesel Products is one.

Thanks dray