15 AMP 3 Way Decora Switch
Three-way switches are always used in pairs and allow you to control a light or receptacle from two different locations. These switches have no ON or OFF markings because the on and off positions will vary as the switches are used.
The three-way switch has three terminal screws. The hot wire from the power source connects to the darkest screw terminal marked "COM" for "common." The other two terminals are called "travelers" and are interchangeable. The switch also has a ground terminal.
The trick in replacing an old three-way switch is to mark the wire attached to the COM terminal before you remove the old switch. Since the other two are interchangeable, you can't get them wrong. If there is a white wire connected to a traveler terminal, it should be labeled with black tape to indicate it is hot.