Our green twinwall duct is used for ducting cable television services and CCTV systems. It is available in one size, 94mm, in 6m lengths. The diameter measurement refers to the inside diameter (I.D.). All dimensions can be found in the table alongside the product image.Twinwall rigid duct is much stronger than flexible duct which makes it ideal for use beneath roads and pathways, or where a deeper underground installation is required. The ribbed external wall ensures that the duct can withstand high compressive forces whilst the smooth inner bore resists any snagging.You should always choose a diameter that allows plenty of room within the duct to allow the cable or cables to be drawn through smoothly. All lengths come with an integral coupler, which enables two lengths to be connected together as required.