ISO 10303-STEP is now widely used as a product data exchange standard. It provides all necessary product-related information. The implementable parts of STEP are known as application protocols (APs). Each AP consists of several conformance classes (CCs) which are required to be implemented in order to be conformant to that particular AP. Though these CCs collectively supply all necessary product information, they are not structured well so that a user would know exactly which CCs are to be implemented to carry out any particular functional analysis (e.g., tolerance analysis). In this study, functionality-based conformance classes (FCCs) are developed to organize the current CCs in order to support different functional activities at different stages of product life cycle. This is accomplished by (1) identifying the required information for different functional activities, (2) grouping the information into hierarchical layers, and then (3) mapping the information to available STEP resources. The required information that is not available in STEP has been mapped to new STEP constructs using EXPRESS-G language. Following the concept of DEX/template, several templates that are repeatedly used small information groups are also introduced in order to create manageable sets of data constructs. In this study, the FCCs for 1-D tolerance analysis are developed by enriching the available STEP information models with GD & T. The use of extended STEP models is illustrated with a case study.