I received two products; one is the one i originally bought, the other is a replacement (when i requested a refund). The first piece I got, a gas spring on it, was supposed to allow height adjustment, but it was too tight and made the height unchangeable. I then asked for a replacement (thinking it was defective). the replacement service is good (not sure if the seller or amazon should be thanked for that). After I received the replaced one, it still has a similar problem. But after trying really hard, I have to say it's finally working. I think some special tools like an electric screwdriver can make this easier. But it's definitely difficult if you use the tool that comes with the product.