I am not sure where to place this I was wondering how most here select the materials for a project Do you have a handbook of different material properties ? Just experience. What you have handy. What is cheapest that you think will work ? Where do you get your materials? If you have some mystery metal do you try to determine what it is? Maybe I'm just making this too complicated. Did some research and thought that vespel might make a good material for a steam engine piston. I discovered it was pretty expensive. Invar may also be an interesting material but not sure where I can get a small quantity. Also wondered how hard invar is to machine.