1. Whether there is a transmission device from the prime mover to the universal coupling. If there is a transmission ratio, it will be output by several shafts after passing through the intermediate transmission device, that is, whether there is power split. Consider the type, power and speed of the prime mover.

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2. It is necessary to consider the type of prime mover and the load category of the optional cross-shaft universal coupling to transmit load: one-way constant load, pulsating load or two-way alternating load. What is the installation status of the universal coupling? Horizontal, vertical or inclined installation. It is necessary to make the axis bend angle less than 3 degrees as much as possible, if oblique installation is necessary, determine the horizontal and vertical angles.
3. Considering the working environment of the prime mover, whether it is affected by harsh environmental conditions such as high temperature, dust, water spray, chemical corrosion, etc., select the corresponding type of universal coupling according to the different use environment.
4. It is necessary to know the required connection form and specific installation dimensions at both ends of the universal coupling, as well as whether there are special requirements such as mounting brackets.
5. What is the speed of the cross shaft universal coupling itself? Whether it needs to be dynamically balanced. Dynamic balance or balance is required, and which other balance quality level is required.
6. Whether there are restrictions on the installation location. What is the specific installation length and whether it needs to be telescopic. When it is required to expand and contract, what is the outward extension of the universal joint in the short state? For universal joints that do not require expansion and contraction, consider the compensation of axial dimension errors, and determine the location for compensation in the system.
Through the understanding of the above prerequisites, gradually determine the specifications of the universal joint shaft, and then determine which structure to choose. The structure forms of universal couplings are 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 type, etc., commonly used is the cross shaft type, followed by the ball cage dragon. In actual applications, it is divided into heavy, medium, light and small according to the transmitted torque. In the same way, the selection of plum coupling is similar. To choose a coupling suitable for the prime mover from so many universal couplings, it is necessary to have a deep understanding of the above-mentioned prerequisites and external influence factors.