Hidden paper clips

These are so cool. Never heard of them until now and decided I should make some. They are hidden paper clips; as you can see, or not see I guess, you don't see the paper clip. Haha. These would make cool bookmarks too, I thought as I was just typing this. These are 3 inches and 2 1/2 inches tall. 

This is the back side. 

Here is one clipped onto a mini envelope to show how it works. Front:

back: