Universal shaft, also known as Maintenance-Free Universal Joint coupling, is a mechanical part used to connect two shafts in different mechanisms, i.e., the driving shaft and the driven shaft, and make them rotate together to transmit torque. As an important part of China's general machinery industry, cardan shaft products are widely used in metallurgy, mining, lifting, construction machinery, automobile, paper making, textile, nonferrous metals, shipbuilding and other industries. With the overall development of China's automobile manufacturing, shipping, construction machinery and other industries, the market demand of China's cardan shaft industry has been expanding, and at the same time, it presents the development trend of high-end and brand.

Universal joints have various products, among which the cross joint is the most commonly used. Universal joint is a mechanical part that connects two shafts in different mechanisms, i.e., the driving shaft and the driven shaft, to rotate together to transmit torque. Generally, power machines are mostly connected with working machines by means of universal joint. In high-speed and heavy-duty power transmission, some cardan shafts have the functions of buffering, reducing vibration and improving the dynamic performance of shafting.

According to the structural form, cardan shaft can be divided into cross shaft type, ball cage type, ball fork type, bump type, ball pin type, ball hinge type, ball hinge plunger type, three pin type, three fork rod type, three ball pin type, hinge rod type, etc. Among them, the most commonly used one is the cross shaft type, followed by the ball cage type.

According to the torque transmitted in practical application of universal joint cross, it can be divided into heavy, medium, light and small cardan shafts. At the same time, according to the relative position and position change of the two shafts, it can be divided into fixed coupling and movable coupling.