Without doubt these are the most popular hatches found on just about every caravan in Australia. This is simply not the case with motorhomes as they are a rarity. Could be worth thinking about. The name comes from the way you can open just one or all sides. There hasn't been many changes over the years and the operating handles are positively old fashioned and newbies do have troubles fathoming out how they work. The aperture size is 660 X 660 so it is nice and large. The large skylight is available in single or double glaze. Frames are either white or cream. They are made in Australia by Australite (Camec). When considering one of these it is worthwhile remembering that you can get three conventional vents installed for the same price. Available from Caravan Accessories and Camec.