A simple joint is the most basic construct of a project. The real power of Digital Pipe Fitter is the ability to combine several simple joints into a single template or to modify a simple joint for a particular application - in these cases you use a utility joint. Utility joints appear just like simple joint windows but instead of being an independent template generator, they utilize the behavior of other currently opened simple joints to create a more elaborate joint or assembly.
Currently the only utility joint is the union joint. An example of the need for a union joint would be a containment vessel where several pipes enter a larger cylindrical container or pipe. In this case, several holes would need to be cut into the vessel. The simple branch joint interface only allows for the intersection of two pipes. If a branch joint is created for each joint needed, then the union joint can assemble those joints into one template to lay out the vessel.