It's quite simple, if you can purchase the parts.
You want to get some very pure Zinc rods, without a steel insert. Might take a while to find such; a welding store is one place to look for, as Zinc rods are used for welding.
Copper is easier to acquire, a basic food-grade hollow copper rod will do.
Saw both pieces to desired length. This depends about your
package, so measure with a string, find a nice snug feeling.
I just checked my tubes; I've cut them to around 2,5 inches.
When you have your rods sawn, you can finally attach then together with some sort of tubing. I favor clear silicone tubing.
Cut the tubing to desired length, that snug feeling. Might take a few tries, so don't cut of too much tubing the first time.
And have some spare tubing at hand, you might want to change it after a while as the ROP works and creates some coloration on the tubing: just a sign that there's connection when it's on your unit and that it works.
I used my ring with some results; didn't get to those 25 spurt ejaculations, but overall I felt it helps with healing. Copper and Zinc, especially Zinc, are good nutrients for the body. Copper balances the action; too much Zinc and you get copper inbalance, which is not desirable.
So, all in all, I think the biggest part for me was to get the parts. I have some copper around, but that Zinc, I can see how it can be difficult to get! Silicone or other sort of tubing shouldn't be too difficult to get, I bought some from my local plastic etc., vendor.
It takes some work, but good things very often do.
I think Supra is quite busy nowadays and only makes some rings on request. So I hope my small insight helped.