An aluminium weld-in bung producing a male AN16 flare port. AN16 is at the large end of the range and is used where you are moving real volume at low pressure: coolant and header tank plumbing, crankcase breather and vent lines, dry sump reservoir connections and large fuel or surge tank transfers. Aluminium construction suits TIG welding into alloy fabrications such as header tanks, catch cans, fabricated sumps and sheet or billet surge tanks. With a port this size the welding sequence matters, so tack at opposing points, work around gradually, and allow cooling between passes so the flange stays flat and the flare seat true.