The Lee Seven5 52mm Adapter Ring is crucial to the Lee Seven5 micro filter system and screws onto the end of your camera's lens. The Lee Seven5 adapter ring fits onto the end of your lens to accommodate the Seven5 filter holder (not included, available separately). Once the ring is in place the holder then clips into place. To find out what size adapter ring you need see the end of your lens for the thread size. This adapter ring features a 52mm thread size.