There are several types of shaft couplings,their characteristics depend on the purpose for which they are used,if an exceptionally long shaft is required in a manufacturing plant or a propeller shaft on a ship,it is made in sections that are coupled together with rigid couplings. A common type of rigid coupling consists of two mating radial flanges that are attached by key driven hubs to the ends of adjacent shaft sections and bolted together through the flanges to form a rigid connection. Alignment of the connected shafts in usually effected by means of a rabbet joint on the face of the flanges.