A male-to-male reducer stepping AN12 to AN10 across the standard 37-degree AN flare on both ends. One size down at the largest end of the common range makes this a low-impact transition, which matters on high-flow circuits like fuel supply on forced-induction builds, dry-sump scavenge and oil cooler plumbing where you have chosen big line for a reason and do not want to throw that away at a joint. Both ends are male, mating to female swivel hose ends or female adaptors. Tighten to a firm seat on the flare cone only; sealant and PTFE tape have no place on an AN flare and can contaminate the system.