This venturi/choke securing screw is Part Number 58 on the Weber parts diagram. It secures the venturi in the carb throat to prevent it moving or working loose. These screws are really pretty unique with a small 'Nub" on the end that fits into a matching opening in the Venturi. These screws also have their Hex Heads drilled so Hold Down Wire can be inserted and Twisted in place as they were originally.