A keystone module is a standardized snap-in package for mounting a variety of low-voltage electrical jacks or optical connectors into a keystone wall plate, face plate, surface-mount box, or a patch panel. Some keystones use a pass-through type connector, where there is a jack on both the front face and the rear side. Others only have a jack on the front and employ a different mechanism for hard-wiring signal cables to the rear, such as a mini 110 block, an insulation-displacement connector, or a crimp or solder connection.