Blue Anodized Aluminum Adapter, -16 Male JIC 37 deg Flare To 3/4 Inch Male NPT, Straight

It’s made to bridge exactly those two thread types, with a -16 male JIC 37 degree flare on one side and a 3/4 inch male NPT on the other, in a straight configuration.

That's exactly what it's built for. One end is -16 Male JIC with the 37-degree flare seat, the other is 3/4 inch Male NPT, and the body runs straight with no angle or offset. Both threads are on the male side, so you'd be threading into female JIC and female NPT fittings on each end. Eaton Aeroquip makes this one, part number FBM2015, and it's intended for hydraulic fluid transfer applications where those two thread types need to meet in a direct line.

This Eaton Aeroquip adapter is suitable for use with a variety of hydraulic fluids. Just be sure to consult the provided fluid compatibility document to confirm it's compatible with the specific fluid you intend to use.