The connector tubes in your 6.7L Cummins is responsible for supplying fuel from the injector lines to the injectors. And as injectors can wear out, so can the connector tubes, as they are also exposed to the high pressure fuel being forced through them. Any time you replace your injectors, it is highly recommended to also replace all six tubes. Replce your connector tubes with the XDP OER Series Connector tube. These tubes are manufactured to be a direct replacement for the factory tubes and includes a new O-ring seal. Sold individually.