inear rails come in basically two types, round and square. The criteria for choosing one over the other is no different than choosing any other machine component; spec out the design, define the system’s objectives, and work from past successes and mistakes. But anyone short on experience can make more mistakes, so a condensed course in selecting the proper rail for any application to keep design errors to a minimum is in order. The best place to start is learning the fundamental characteristics of each type, and adopting those that are most relevant to the application.