This document establishes the default specification operator (see ISO 17450-2) and defines a special specification operator for linear sizes. It applies to the following features of linear size: — cylinders, — spheres, — two parallel opposite planes. Annex C handles the definition of sizes for circles as sections of a cone. Annex D handles the definition of sizes for circles as sections of a torus. Annex E handles the definition of sizes for parallel opposite lines as longitudinal sections of cylindrical tubes in half planes containing a specified axis. This part of ISO 14405 provides a set of tools to express several types of linear size characteristics. It does not present any information on the relationship between a function or a use and a linear size characteristic.