Stainless Steel Adapter, 1-1/4-11-1/2 Male NPT To 1-5/8-12 Male JIC 37 deg Flare, Straight

That's what it's built for. One end is 1-1/4-11-1/2 Male NPT and the other is 1-5/8-12 Male JIC 37-degree flare, so it makes that transition in a single straight fitting. No unions, no couplers, no extra hardware stacked up in your line. The stainless steel construction holds up well in environments where corrosion is a concern, and the straight configuration keeps your flow path clean without introducing unnecessary turbulence or pressure drop.