Beam Central Vacuum System. Ducting fittings available, to build a ducting system, will suit any brand of System.
It is important that the ducting is installed incorporating a sweeping airflow back to the systems power unit. Care must be taken, when using the fittings, that the sweep of the fittings are positioned correctly, with regards to the airflow.
See diagrams with fittings airflow, in Installation Manuals.
Common components of installation kits.

Overlap surround for a rectangular inlet valve

Ducting end cap