After installed this temperature controlled automatic vent opener, your window will be a self opening one. It is solar heat sensitive that open the vent when weather warms up and then closing when it cools down. Really works well in maintain the greenhouse within the preferred temperature range.Features:Compared with the single spring vent, the double one has stronger thrust force, more solid, and much durable.The double spring vent opener can be closed manually.Elongated aluminum cylinder with paint spraying, weather resistant.Solar heat sensitive vent opener, automatic stretch or shrink the vent while the temperature is changing.Stainle steel acceories would last long time use.Aluminum frame looks more lustrous, durable and rust-proof.Easy to install, universal fit for all aluminum frame greenhouse.Auto-opening temperature range is adjustable from 15-25(60-77) by turning the cylinder. (Clockwise for higher, counter-clockwise for lower)Maximum opening at about 30/86(depending on adjustment and load).Suitable for the vents weighting up to 7kg/15lb. single spring kit BSpecifications:Material: Paint Spraying IronColor: BlackStar open at:15-25 (60-77)Fully open at: 30/86Max open distance: 45cm/17.71inchLoad bearing: 7KG / 15lbCylinder Length: 33.8cm / 13.3inchPackage Size: 38*10*5cm / 14.96*3.93*1.96inchPackage Weight: 520g / 1.14lb single spring kit W Specifications:Material: Paint Spraying IronColor: WhiteStar open at:15-25 (60-77)Fully open at: 30/86Max open distance: 45cm/17.71inchLoad bearing: 7KG / 15lbCylinder Length: 33.8cm / 13.3inchPackage Size: 38*10*5cm / 14.96*3.93*1.96inchPackage Weight: 520g / 1.14lb Temperature Sensor Specifications:Material: Aluminium, Stainle SteelColor: BlackStar open at: 15-25 (60-77)Fully open at: 30/86Length: 33.8cm / 13.3inchPackage Size: 34*1*1cm / 13.38*0.39*0.39inchPackage Weight: 140g / 0.3lb Double spring kit Specifications:Material: Aluminum+SSItem Weight: Approx. 376g / 13.26ozPackage Weight: Approx. 439g / 15.49ozPackage Size: Approx. 38 * 9.5 * 4.5cm / 14.96 * 3.74 * 1.77inPackage List:1 * Vent Opener1 * Package of Acceory1 * Manual (English)Note:Do not heat to more than 50(122).Do not dismantle the cylinder.Cooling the cylinder for 24 hours before installation.