DOUBLE SPRING -- Dual Spring Solar Vent Opener with Stronger Force, up to 15lbs. If 1 Set is still not enough for your window, you could use two window openers together.PREMIUM QUALITY -- The window opener is made of high quality aluminum alloy. Durable and rust resistant in damp environments Long service life.EASY TO INSTALL-- Easy to fit onto your Greenhouse vent or window using supplied screws and clamps or your own fasteners into pre-punched holes.NO ELECTRICITY NEEDED -- Uses solar energy, open or close the greenhouse vents as temperature rises or drops and clamps to greenhouse bars.SUITABLE FOR MOST GREENHOUSES -- This opener will automatically open and shut your greenhouse window to maintain the best growing temperature and preventing your greenhouse from overheating.Specifications:Lifting capacity: max. 7 kg\/15lbsLifting height: max. 45cm\/18''Temperature range of approx. 20 - 25 CMaterial: steelBox contents:1 x Automatic Window Opener KitNotes:Do not use this opener anywhere the temperature will exceed 50 (122F)Please your greenhouse window can be opened freely by at least 45cm (18\