Sized for AN8 — the step up most builders take for higher-flow fuel feeds, oil cooler lines and transmission cooler circuits. The cap threads onto the male AN8 fitting and seals against the 37-degree cone, so the joint needs no washer or sealant and can be broken and remade without replacing anything. Practical uses include blanking a second outlet on a fuel filter or surge tank, sealing a cooler port while the cooler is out for repair, and protecting open lines on a stripped car. It caps male AN8 threads; female AN8 ports require a plug instead of a cap.