The one we used was a bit of an odd ball. I think it came from Bob's house of bass. I remember it being hollow because we were so worried about crushing it with his thumbscrew, my current aluminum endpin though is hollow.
I am about to try a solid CF rod on my bass. Found just finding a piece of 10mm carbon fiber is much cheaper then something that is an endpin rod
depending on the results I might try something wooden next. Any suggestions on what kind of wood might be the best ? Right now I am think either a strong maple or maybe lignum vitae (if I can find it).