The Helios F 355 is an adapter designed to facilitate the connection of 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 includes four corner holes that correspond to the attachment points on the shutters, ensuring a secure fit. The round connector portion is mounted onto the fan casing and fixed in place using self-tapping screws, providing a practical solution for transitioning from square to round ventilation components.