Ventilation pipes are purchased from HorecaTraders
HorecaTraders provides transitions that allow you to connect two spiro tubes with different diameters. A spiro tube adapter has two round connections in two different diameters. For example, you can choose a 300-350 Ø adapter or a 250-350 Ø adapter.
The HorecaTraders Conductor Ø 300-350 has a good value for money and a solid design. Hence, this version is widely used in catering establishments.