This paper presents a strategy for the automatic generation of customized libraries of form features and basic design shapes for CAD systems. Generation of the initial libraries involves the application of a recursive procedure on each model stored in a CAD system. The procedure alternates between a feature extraction stage and a coding stage. In previous coding efforts, objects and form features were classified on the basis of their shape characteristics. As a result, classes of objects and form features were defined. A customized code is then developed to sort objects and form features, when encountered, into one of the predefined classes. In this work, for the purpose of coding, classification is performed at the level of loops, with a loop defined as a cyclic set of edges. Therefore, predefined classes of objects or features are not generated. A code is then developed to convey the loop information. The generation of a loop code for all loops on an object results in a numerical pattern that characterizes the object's (or feature's) topology, constrained by the convexity of its edges.