Abstract: A container system includes first and second container bodies and a connector for holding the container bodies together as a container sub-assembly. The container bodies each define external connector passageways, which are aligned co-axially for assembly. The connector passes through the passageway of the first container body and engages with a thread in the passageway of a second container body. A connector head engages the first container body to clamp the container bodies together. The sub-assembly is affixed to a supporting structure by a fastener having a threaded shaft passing through the connector to clamp the connector to the mounting formation. The clamp load is borne by the connector to prevent the container bodies being damaged when the fastener is tightened. The container system is particularly suited for providing twin tanks for fuel and a fuel additive on a vehicle or agricultural machine.