Keystone jacks are keystone module connectors used in data communication and LAN wiring. It is the female connector that is usually mounted in a wall plate or patch panel and is connected to the matching male connector, called the keystone plug. A keystone module is a snap-in package that is used for mounting various types of low-voltage electrical jacks. It can also be used for mounting optical connectors into the wall plate or patch panel. http://www.cobtel.com/keystone-jack/