Extendable Cavity Wall Vent Blue / Black Air Brick 9" x 6" Inch The Manthorpe G941 Thru...air Single Airbrick with 4 inch pipe. Allows for an extraction system to be conveniently built into the brickwork. Eliminating the need for retrospective core drilling. Extendable telescopic pipe to suit the thickness of the wall and ducting connection. Extends to suit wall thickness of 300mm - 440mm. Provides easier and quicker installation to match the demands of on-site construction. Provides a maximum equivalent area of 7300mm² of free air space. Meets NHBC requirements for the control of condensation in buildings. Other colours and sizes available in our shop.Technical Imformation Geometric Air Flow 7,300mm² External diameter 103.5mm Minimum overall length 300mm Maximum overall length 440mm