I used 3/8" tubing, which is what comes with the Dragon kit from PSI. I used a ten inch length of tubing so that I can cast the whole length and then cut it to size for three pens. I promised my daughter one, I'm doing one and I'll have one for sale. I'm doing my daughter's pen stock, but plan on doing a bit extra to mine. Many years ago I had another hobby, scale modeling. I plan on cleaning up this kit considerably and then getting out the oil paints and painting up the Dragon kit in much the same way we did figures for contests. I used to compete in the scale model contests country wide and did a pretty good job of it winning Regional and National events. I was mostly in to modern aircraft, but did do almost all of the different categories at one time or another. I'm not as good at it as I was as it is a perishable skill and I haven't kept up with it at all. We'll see what I have left in it though.