Steel Adapter, 0.38 Braze Port To Male O-Ring Face Seal, Straight

The braze port end on this adapter is sized for 0.38 inch tube OD, so yes, that lines up with standard 3/8 inch tubing. The other end is a male O-ring face seal at 11/16-16 thread, which is a 6 series ORS connection. Seal part FF9446-12 is included, so you've got what you need to make a complete face seal connection without hunting down a separate o-ring.

Eaton Aeroquip built this part with some pretty demanding environments in mind. Listed applications include marine and military use, chemical processing, pulp and paper, food and beverage processing, and offshore drilling. If your operation falls anywhere near those categories, you're well within the intended use range. For lighter-duty or general industrial work, it'll still do the job, but those are the target environments this series was developed around.

Eaton Aeroquip specifically lists marine applications among the intended uses for this adapter, along with chemical processing and offshore drilling, so it should be suitable.

You are on the right track. It is a straight steel adapter that goes from a 0.38 braze port on one end to a male O-Ring Face Seal (ORFS) connection on the other, which is a common way to transition from a brazed-in tube connection to an ORFS hydraulic hookup.