These suction cups fall off anything they are attached to. I purchased what appeared to be an identical one about a year ago and it works very well so based on this excellent performance I bought 5 more under this order but even though they were brand new and in the packaging these ones appear to have manufacturing defects. I took a picture of my old one next to these new ones and you can see a very different look to the rubber. The supplier says he will talk to the manufacturer. I am going to try to smooth the rough rubber somehow in my work shop but not a good experience so far and no offer to refund my costs were made. In the attached picture the good one I owned previously is to the right. You can see the irregularities on the bad one to the left. All five were poor and only one stuck on for awhile.