[practicality ]This is a replacement cylinder for automatic window opener[excellent performance ]High sensitive, automatic respond to weather changes, so you don't need to stay near the greenhouse[how it works ]Non electric, uses solar energy, open or close the greenhouse vents as temperature rises or drops[applicablity ]Great for most greenhouse to open or close window automatically[high quality]Time and labor saving, also can supply a better temperature condition of plant's growthsize: 33.5cmMaterial: galvanized sheet aluminumcolour: blackPackage Contents:1 x window openerOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.