Vibrant 1.5-inch OD aluminum tank weld bung includes a black anodized threaded cap and O-ring, made from 6061 billet aluminum. The improved flange design resists warping during welding; caps are available polished or anodized black and are intended to thread on for sealing. The product notes explicitly caution against welding the bung with the threaded cap installed.
Vibrant 1.5in OD Aluminum Weld Bungs w/ Black Anodized Threaded Cap (incl. O-Ring)