This is a one-piece, wide-mouth canning jar lid that can be printed on a Rep-Rap, Makerbot, or similar 3D printer. I made it to close a jar of hydrochloric acid, which will attack metal but not ABS plastic. The threads work very well.Print upside-down, with the flat top stuck to your build platform and the threads facing up. If it doesn't fully seal the jar, you can try smearing or drizzling a little paraffin wax around the inside edge of the lid, where the jar lip touches. Both ABS and paraffin wax have good resistance to hydrochloric acid, which is what I made this lid to contain.