The square duct to wall flange spigot is screwed into, or glued onto, the area around the outlet point in your extraction system. The rim can then be used to attach ducting using a duct clip or duct tape.

To mount the duct to wall spigot, start by drilling enough holes into the flange area to ensure that the spigot can be properly secured to the wall. This should always be carefully undertaken by somebody with the appropriate skills. Then, screw it into place, so that it sits flush over the outlet point. Ducting can then be fitted over the rim using a duct clip.