The Shieldmaster 500-880mm is an adjustable length of twin wall pipe that is best utilized to pass the system through an external wall. This component has a locking band that you can use to quickly and easily connect it to the previous Shieldmaster part and additional insulation.
You won’t require any additional sealants or silicone to seal all the joints. It has a unique push-fit locking system to make connection and disconnection very simple. The quoted diameter is the internal diameter and the surrounding insulation makes it 2” larger.