A general classification of the shape of a part. Parts are often first classified by their thickness as being either flat, thin-walled, or solid. Thin-walled and solid parts can be further classified by the basic shape of their outer surface, being either cylindrical, cubic, or complex. The part shape can help to determine compatible manufacturing processes. For example, flat parts are best suited to sheet metal fabrication, thin-walled parts are typically molded or cast, and solid parts are most often machined or forged.