Wallbarn extension shanks are designed to fix up with the drainage outlets to increase the reach into the parapet wall or drainage channel. Often the ducts and channels will have to pass through a long run of concrete before reaching a suitable area to install the HDPE drainpipe, so an extension of a fully waterproof sealed connector will be required. These extension shanks are specially designed to fit in with the full range of Wallbarn circular outlets. They are made from TPE but can still be used with EPDM and PVC outlets. They are manufactured to a slight cone shape, so the end of the circular outlet slots inside the top of the extension shank. The two membranes are bonded together using silicone adhesive. FOR HDPE PIPE 111 106 116 240. Please note: Installers of PVC waterproofing systems should always inform waterproofing manufacturer before using these two materials together in order check the status of the warranty. Please also note the TPE needs to be smaller than the HDPE drainpipe. Dimensions Length: 240mm. Outer diameter of the pipe at the top: 74mm. Inner diameter of the pipe at the top: 69mm. Inner diameter of the pipe at the bottom: 64mm.