Hi Daniel. Well, most steels would suffice in my opinion. If it's not meant as a proffessional tool to be in daily use, and last for ever, any steel should outrank the softer brass in the NRV. I have used steel with a carbon ratio that allows it to be hardened, but as I think I said somewhere; it's actually overkill. You could try a suitable screw that's large enough to fit the pump tube if it's mainly a question of getting hold of things you already have lying about.
Thanks for your reply. With the risk of sounding like an idiot but I do not understand how the prototype tool head have been fastened to the threaded rod in the picture above. I mean if a threaded a M8 hole is drilled into the prototype tool head and the threaded rod is inserted clockwise. Will engaging the NRV counter-clockwise not result in the tool head getting unwinded? Is the nut next to the tool head the answer to this mystery or perhaps the hole is drilled with a left-handed thread?
Yes, that nut is the answer. It locks the head, and should of course be tightened very hard. It could also be a good idea to lock things even further with the strongest Loctite, or any other chemical threadlock. Or why not weld it together? Mind you, this was only a test tool to see how the idea would work. But it did actually work well enough despite its flimsy look, so as a makeshift tool, it's quite allright.
