These connectors are perfect for reducing 13mm pipe down to 6mm pipe, when using large systems. They are inserted in-line at the point where an AQUAvalve or aquaPot is positioned. They provide a water tight connection unlike many other types of reduction fittings. They work in exactly the same way as the AutoPot Cross Connector 13mm to 4mm  but this fitting has one connection for 4mm pipe whereas the cross connector provides two connections for 4mm pipe.