Except for stainless steel, fittings can be made of other materials for different features such as hydraulic hose fitting, metric hose fitting, BSP hose fitting, JIC hose fitting, etc. Of course, a fitting must work in connection with a flange including hydraulic system flange, hydraulic flange, 37°flare flange, retaining ring flange system and so on. http://www.jrfluid.com/hydraulic-hose-fitting/bsp-hose-fitting/