Normally I don’t post photo’s that aren’t my own, but I feel this illustrates a point very well. What you’re looking at is a museum setup of a step-by-step telephone exchange. These were probably taken from a small rural central office, and you can see it’s composed of Strowger mechanical switches.
Note the rotary test sets on that shelf towards the left. The orange one indicates that it’s designed for use in a central office, so the test clips are suited for that task (as opposed to field units which are typically blue).










