Nickel Plated Aluminum Adapter, -06 Male JIC 37 deg Flare To 1/4 Inch Male NPT, Straight

That's exactly what it's built for. One end is a -06 male JIC 37-degree flare and the other is 1/4 inch male NPT, and the straight configuration keeps everything inline without adding any angle. Manufactured by Eaton Aeroquip under part number FBE2004, also cataloged as C1ZW74, so it should be easy to cross-reference if you're pulling from a parts list.

The nickel plating on this Eaton Aeroquip adapter is there to provide corrosion resistance, so it should be well-suited for use with a broad range of hydraulic fluids. You can check Eaton's fluid compatibility reference for specific fluid types.

Function-wise, it is a straight adapter that bridges two different thread styles: a -06 male JIC 37 degree flare on one end and a 1/4 inch male NPT on the other. It’s used when you need to transition from a JIC flare connection to an NPT threaded port in an inline setup.