Proliferation of plastic in parts, and the ability to mold such parts of great complexity at little cost penalty, has resulted in growing use of integral attachments (or so called snap-fits) in designs. The diversity of integral attachment features and the potential applications of this assembly method have made it appear that design possibilities may be unbounded. This paper extends an “attachment level” methodology first articulated by researchers at General Motors by enumerating all possible design options for 2-D (rectilinear) and 3-D (prismatic) polyhedral as well as 2-D and 3-D curvilinear parts using a recently developed hierarchical classification scheme. It was found that there are only 343 possible interface combinations that will allow attachment, of which only 150 are totally unique if one recognizes the interchangeability of attachment features between mating components comprising the assembly. Thus, for a seemingly infinite or unbounded group of possible real integral attachment applications, the choices are, in fact, limited to a quite manageable number. This allows designers to truly optimize a design by considering literally every possibility after working down through the classification hierarchy.

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