pen tube

I bought a few of these at a pen show years ago. They can twist telescope to fit a longer pen. I need more and can’t find them anywhere. Does anyone know what they are called or where to find them?

Hi, I have been using brass tubes that come in the kits since I started. I find however that sometimes the material can get damaged on the insides when I squaring the ends. This has caused some instances of the pen not twisting easily as the refill catches on the insides of the tube. I...