Maybe 5-100PSI depending on the trans and how it's set up. Not much, but the chemicals in the oil and the heat need to be taken into consideration when choosing hose material and construction. Even the rubber lined AQP style hose is questionable.

There are -6 x 1/8" NPSM fittings available which rely on a gasket to seal vs. pipe thread. Helps eliminate the possibility of cracking a case from over tightening NPT fittings.