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It's something I saw on Taobao's "try this for practically free" section (where new products get introduced) and tested. They're advertised as being able to hold up to 0.9kg for 2 small ones to 7.2kg for 4 large ones. Let me see if I can find a picture.

That's what they look like in package. The sticky backing is a weird form of "gel tape" that sticks to almost anything, but can be removed by just stretching (at the point where you see the arrows) without leaving a mark. Here's how they're used: