Gas Springs provide silent, effortless, precise and reliable movement that is unattainable with stays using metal springs or friction to control motion. The stays, usable on both down-moving and up-moving lids, are simple to install. The mounting brackets are applied to the case and the lid separately and the body of the stay just snaps on. Pneumatic stays are rated by closing force in pounds. You will need to find the correctly rated stay for your project. Too much will not allow the lid to close properly. If your lid is wider than 36", we recommend two stays. Comes with screws, mounting plates for left or right installation and instructions. Sold as singles.Formula to determine correct stay:X = 6 x W x H / 1000X = closing force in lbsW = weight of lid in KG (2.2 lb per kg)H = height of lid in mm (25.4 mm per inch)ExampleA lid that weighs 11 pounds (5kg)And is 8" high (203 mm):X = 6 x 5 x 203 / 1000 = 6.09 k