The Helios F 400 is an adapter designed for connecting square ventilation shutters from the VK, RVK, EVK, and RAG series directly to round ducts or fan connectors, such as those from the HQ/HW series. It features four corner holes that align with the shutter attachment points, allowing for secure mounting. The round connector is positioned on the fan casing and fastened using self-tapping screws, providing a reliable solution for transitioning between square and round ventilation components.