Listen to Reviews. I decided I would give it a try despite bad reviews. thought it was the way they used it. 2 can be used when blocking objects to prevent them from moving. and use 4 at the same time? Almost impossible if you don't jack up the car. The reason I bought them was to avoid it. makes them almost useless or difficult to use on a regular concrete surface, or at least for my use. I see that some reviews can make them work, but not in my case. Save your money, use blocks or bushings instead if possible