Anodizing Tubing

[dancollinsjr]

I have several pieces of 6061 tubing 1" to 2" in diameter, 1 to 5 feet long. Each piece has a few small holes. I only want to anodize the exterior of each piece. How do I mask or "stop off" the interiors? Coatings, plugs or ?

[mcaswell]

http://www.caswellplating.com/kits/maskit.htm