A rotary joint is a mechanical device that allows the transfer of fluids or gases between stationary and rotating parts. It is commonly used in machinery where movement is essential, such as in industrial equipment, robotics, and automated systems. Rotary joints help maintain a continuous flow while accommodating the rotation of components. These joints can be designed for various applications, including hydraulic systems and pneumatic systems. They come in different types, such as single-pass and multi-pass, depending on the number of fluid paths required. Proper selection and maintenance of rotary joints are crucial for efficient operation and longevity.