If you have an Air Zenith OB2 Compressor and want to step the leader line down to 3/8" NPT or 1/4" NPT (instead of using the supplied 1/2" NPT fitting) then this AN to NPT adapter is what you need!
Air Zenith OB2 compressor comes with a pre-installed -8 AN to 1/2" NPT adapter. This is a direct replacement.