it's controlled gas spring ,to regulate the angle of chair ... will provide best service to you.2,High quality and competitive price3,We delivery soonif you want ... Features: 1, Gas: Nitrogen filled inside. 2, Color : black,silver,or as clients request. 3,Quality: We can ... gas spring is up and down, it's soomth opration without noise. 5,Safe and easy installation. 6,Resonable price, excellent quality ...