When connecting two shafts, to perform a complete centering is very difficult work. It is also difficult to maintain the condition due to a deflection of shaft caused by machine operation, thermal expansion of shaft, bearing block strain after a long-term use or bearing wear. However, theses problems can be solved by choosing the appropriate flexible coupling in accordance with the intended use. As well as general-purpose motors, a wide range of products corresponding from servo motors for ultraprecision controls to engines that generate a large vibration and impact are available.