1.If only use Trunk Spring Lifting Device pls take care when you open the trunk .it is powerful . 2.If your trunk have Silencer cotton ,use 2 pcs .If your car have no Silencer cotton or the Silencer cotton is very small ,just use 1 pc. 3.When installing, please install one to test the effect, if you can open to the height of 1/2,it works great , it is not recommended to fully bounce. 4. Springs can fit any vehicle ,free angle adjustment .