A male-to-male reducer joining an AN16 flare to an AN10 flare, both on the standard 37-degree AN seat. AN16 is used on genuinely high-volume runs, typically dry-sump scavenge lines, large oil cooler circuits and big fuel returns, and this fitting lets such a line meet hardware built with AN10 ports. A three-size step is significant, so put it where the flow has already done its work rather than mid-run in a section you need to keep unrestricted. Both ends are male and require female swivel hose ends or female adaptors to mate. The flare cone makes the seal, so tighten to a firm seat and use no sealant.