These Cardan style universal joint couplings are suitable for electric motors & I/C engines up to 2.5cc. Although similar to other couplings on the market, they are not to be confused with weaker plastic joints but are precision made of very strong nylon. The inserts use about 26 splines to make a very strong non-slip connection. By using any combination of brass inserts it is possible to join any motor to any shaft, or shaft to shaft. It's also possible to use the double insert to make a double universal joint.