A carburettor inlet adapter pairing an AN6 37-degree flare with a 5/8*20 thread. The 5/8-20 inlet is the fuel entry thread on square-bore and several older four-barrel carburettors, and this adapter replaces the original inlet fitting so a proper -6 AN braided feed line can be run in place of rigid factory plumbing. That makes routing far easier in a swapped or rebuilt engine bay and gives a joint that can be undone and reused. AN6 is the sensible feed size for most carburetted street and club-level engines. Check the actual inlet thread on your carburettor first, as 5/8-20, 9/16-24 and 7/8-20 inlets are not interchangeable.