Angular and Parallel misalignment and shaft axial movement needs to be factored into all coupling selections. Some couplings can accommodate very little or no misalignment whilst other styles are quite tolerant. Generally couplings with rubber or plastic inserts will allow for more misalignment than full metal couplings, although some full metal designs can be very tolerant of misalignment. In determining the material compatibility a number of criteria need to be examined, including but not limited to... Is the material selected capable of withstanding the high or low temperature associated with the application? Are there any chemicals present that may corrode any of the materials used? The effects of galvanic corrosion if planning to use dissimilar materials for shaft and coupling. This is beyond the scope of this document. If the application has a lot of vibration it may be necessary to use a coupling that incorporates rubber in the design. Full metal couplings are best suited to smooth running applications. Another consideration in vibratory applications is the locking method. You may need to consider how you are going to prevent the coupling from vibrating loose from it's attachment to the shafts. It almost goes without saying that physical space available within the application should be taken into consideration when choosing a coupling, but it is surprising just how often this factor is overlooked.