A male-to-male reducer with an AN20 flare at one end and AN16 at the other, both on the standard 37-degree AN seat. AN20 is about as large as automotive AN plumbing goes and is reserved for very high-volume work such as large dry-sump systems, heavy oil cooler circuits and bulk transfer lines. Dropping only one size keeps the restriction at the joint minimal, which is the entire point of running plumbing this large. Both ends are male and mate to female swivel hose ends or female adaptors. Fittings this size need proper spanner access; plan the assembly order before you build the hoses, and use no sealant on the flare.