[MrForbes]

A limit switch is any switch that is used to detect an "end of travel" condition.

In other words, it's a functional description, not a physical description. The GDC kind of messed up when they specified what part we can use, based on a functional description, rather than a physical description.

But what they appear to mean is what's commonly known as a "microswitch", which is a brand name that has become a generic term for a small rectangular snap action switch, usually with a lever that activates it.

Radio Shack sells a few of them. We used them on our minibot. The one with the roller on it works well for what you want to do.