Features are higher-level modeling entities that encapsulate multiple lower-level entities and relations into one easily usable unit. It has been shown previously that having CAD-like features in function modeling can increase the ease of modeling, model consistency, and reasoning. This paper presents and illustrates a protocol for extracting function features that can be used frequently in computer-aided function modeling within a given technical domain, and formally defines those features using graphical templates and grammar rules. A comprehensive set of six function features is thus created for the Thermal-Fluid Systems domain. Extendibility of the protocol is then illustrated by using it to extract two additional features from a different domain. The features thus produced, and their variants and usage in modeling are also discussed.