Hexagonal and piston rod & adapter hydraulic cylinders are offered under the category of hydraulic fittings. What are hydraulic fittings? The use of these fittings is to connect hydraulic hoses to components such as hydraulic cylinders, pipes, tubes, or assorted hydraulic hoses. Their wide range allows fluid to flow, change direction, divert, or mix. The application through which the hydraulic fittings confirm the sealing is via on the thread or by using an O-ring. How to install hydraulic fittings? First, find the best fitting as per your application. Then simply remove the older fitting and install the new one.