The aerodyne cowl has been in constant production for about 50 years and has abundantly proven its worth in curing downdraught, showing that the laws of aerodynamics dont change. As wind from any direction passes through the cowl the unique venturi shaped surfaces cause a drop in air pressure which draws smoke and fumes up the chimney for dispersal to atmosphere. Designed to fit chimneys and flues 150mm x 250mm (6 - 10) internal diameter. Fixed via four hook bolts and wing nuts. Fully assembled. Suitable for use on solid fuel systems - logs, coal, peat - not gas. Manufactured from 1.2mm thick high grade aluminium alloy. Please note the chimney is not supplied. This item is natural aluminium.