AN6 is arguably the most-used size in performance plumbing, covering fuel feed and return on most naturally aspirated and moderately boosted engines, turbo drains and power steering work. That popularity means spare AN6 ports show up everywhere — on fuel rails, filter housings, pumps and regulators. This cap screws over the male AN6 fitting and seals on its 37-degree flare, giving a leak-free blank that can be removed and refitted as often as needed. Handy during commissioning, when you want to pressurise part of a system while another branch is still unfinished. Fits male AN6 threads only.