This paper describes the development of an expert system for selection of multidiameter drills. These drills are used for stepped hole drilling operations. The structure of an expert system for multidiameter drills is outlined. The aim of this development was to establish a framework for an expert system which uses existing tools to combine a rule-based knowledge base, a database and online help including diagnostics working together within the Windows environment. A new intelligent system structure, operating in the Windows environment, has provided more flexibility and user friendliness than other similar systems.