for the life of me I can't find these anymore. I need to make a piece of DOM longer and I know I saw someone selling a slug that slides inside so you can weld 2 pieces together but can't find them now...Anyone know where I can find some?
Yep just use spare tube you have.
I typically make the "plug" as long as I can reasonably make it and put at least two if not more rosette welds in it.
