I just made some for a big F-18. They had to be 22" long. I used a 20" piece of Stainless Steel allthread. Slide coated the allthread with epoxy, slipped a carbon tube over that, coated that with epoxy and slid another carbon tube over that. I don't have the exact sizes of the tubes but The inner on the first tube was exact fit for 4-40 rod( .110) the second slid over the first with absolutly no play at all. The overall diameter of the final tube is about 5/16. When the epoxy dried you couldn't bend these things. The ball links just threaded on to the ends. I used some of the Skymaster 4-40 metal bearing ball links. I made the same for the rudders too. which only needed the first carbon tube. How long do you need to make yours?