A keystone jack module is a standardized snap-in package for mounting a variety of low-voltage electrical jacks such as TV, Phone, LAN, Data, BNC, RCA or optical connectors into a keystone wall plate, surface-mount box, or a patch panel. Keystone modules have a commonly popular standardized rectangular face of 14.5mm wide by 16.0mm high and are held in place with a flexible tab. This allows them to be snapped into or out of a mounting plate with correspondingly-sized rectangular holes, called ports. All keystones, regardless of the type of jack they carry, are interchangeable and replaceable. This is what makes Keystone a popular choice in today's installations at Home or Office. Some keystones use a pass-though type connector, where there is a jack on both the front face as well as the rear side. Others only have a jack on the front and employ a different means for hard-wiring signal cables in the rear, such as a mini 110, insulation-displacement connector, crimp or solder connection.