In this chapter, we covered more advanced assemblies, and introduced the concept of component tolerance and fits. We then went on to explore what it means to design for assembly. The majority of this chapter focused on applying these newly learned principles to the practical example of designing a modular unit of an office building facade composed of interchangeable components. Although our example only covered a brief number of possibilities, it can be used as a framework to create infinitely more of them; however, all these things take time to design. We could dramatically reduce design time if we had some sort of library of already designed models that were ready for printing. In the next chapter, we will introduce you to this library, which is found on Thingiverse and GrabCAD. Welcome to the community.