An aluminium weld-in bung that gives you a male AN4 flare port wherever you need one. AN4 is the small end of the range, so it suits low-volume lines rather than main feeds: oil pressure gauge and sender runs, vacuum and boost references, clutch lines, turbo oil feeds and small breather take-offs. Being aluminium, it is meant for TIG welding into aluminium fabrications such as billet or sheet surge tanks, alloy sumps, catch cans and header tanks, not steel. Tack it in stages and let it cool between passes so the port stays round and the flare seat stays true. Do not over-tighten the mating fitting.