In general, wording is not permitted on a drawing, unless it is a flow diagram. Numbers are used to indicate the various parts of a product and these numbers are referred to in the description and, sometimes, in the claims. Further, patent drawings need to be clear and uncluttered and should not, in general, include any markings indicating dimensions or materials used since these may limit the scope of protection to those dimensions or materials. Engineering drawings are seldom suitable and special drawings usually need to be prepared for a patent specification.