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/18Temperature 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)Do not apply excessive loads by locking or covering windowDo not dismantle the cylinderThe opener CANNOT stop by manual