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.Stainless steel accessories 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 weighing up to 7kg/15lb.