Got my zinc from Mcmaster today. The zinc was $10.54 counting $4.00 shipping and it yields two 3" zinc bars for 2 ROPs. I tried bending the zinc a little so it would lay better against the skin and be more comfortable. This works nicely with the copper but the zinc is brittle and starts to crack. I am quite happy with my two new ROPs. I figure with all the costs of materials and shipping, they cost me about $7.50 each and I still have copper and latex tubing for more. The cost per ROP could be quite a bit less by ordering multiple zinc since the shipping would not be much, if any, more (the box was almost empty and very light).