This paper describes modeler independent application programming interfaces called adaptors. A solid modeler is augmented with an adaptor so as to provide a standard procedural interface to applications and function as a geometric server. Adaptors give the applications portability and free the application programmers from the details of specific modelers. Adaptors have been developed at USC for two different modelers, PADL-2 (a Constructive Solid Geometry system) and Parasolid (a boundary modeler). The issues raised in adaptor development and their solutions are discussed. Adaptors are routinely used at USC in a distributed environment where a solid modeler augmented with an adaptor, an application, and a renderer run as separate processes and communicate with one another through local area networks.