A B-double consists of a prime mover towing a specialised lead trailer that has a fifth-wheel mounted on the rear towing another semi-trailer, resulting in two articulation points. It may also be known as a B-train, interlink in South Africa, B-double in Australia, tandem tractor-trailer, tandem rig or double. They may typically be up to long. The fifth wheel coupling is located at the rear of the lead (first) trailer and is mounted on a "tail" section commonly located immediately above the lead trailer axles. In North America this area of the lead trailer is often referred to as the "bridge". The twin-trailer assembly is hooked up to a tractor unit via the tractor unit's fifth wheel in the customary manner.