A new jig or clamping device often needs adjustment and locking screws, and here’s how to make your own. Take a machine screw of whatever length you need, preferably with a hexagonal head, and epoxy it into a metal bottle or jar cap of appropriate size. Some caps come with a knurled edge which gives a good grip. If I have to use threaded rod to get the length needed I put a hexagonal nut on one end and lock it with epoxy or a sharp blow with a hammer. Be sure to have the screw head centered in the cap and perpendicular to its base. It’s also essential to clean the inside of the bottle cap of any residue from the contents of the jar. You may want to file small grooves in the rim of the cap to prevent slippage.
– Frank Penicka
Mount Pearl, Newfoundland, Canada