Brass Push Tube Fitting, 0.25 Inch Tube OD Run & Branch To 3/8 NPT Male Swivel Run, Tee

Brass offers decent corrosion resistance for typical industrial environments where pneumatic systems are common, so it should do fine with incidental grease. For constant or heavy exposure, though, you might want to explore a more specialized fitting.

The push-to-connect ports are for 1/4 inch tube OD on the run and the branch, and the run port has a 3/8 NPT male swivel thread.

That's exactly the setup this fitting is built for. The two push-to-connect ports take 1/4 inch OD tube on both the run and branch sides, and the swivel run port threads directly into a 3/8 NPT male connection. The swivel lets you get the fitting seated in the port first and then rotate it into position without twisting the tubing or disturbing anything already assembled. No extra adapters needed for that combination.