I use tubes from my local kite shop. The only problem is the ID of the large tube is .010" smaller than the next tubing size down. I have a 13mm reamer that will open up the largetube to .511". The reamer is not long enough to go all the way through the 16" tube. It leaves a 1" section in the middle unreamed, so the center doubler tube won't fit. I just sand down the doubler tube on the belt sander till it slide in nicely.
