I have a student who is tearing his thumbs up by constantly picking at them when he is not engaged with something. Another teacher suggested this Fidget Cube, so I went on Amazon and bought several. There are a few different vendors on Amazon that you can choose to purchase from. I liked that they were under $5 a piece.
The student LOVES it! He prefers the side that does the clicking (reminds me of someone clicking a pen), but he will move on to a different side after a time. It's small enough to put in his pocket or attach the string to a keychain, wrist, or something else. But the best part of all of this is that he is NOT picking at the thumbs so they will heal!!
I'm allowing him to take it home, but reminded him he has to have it every day at school! It took less than a minute to introduce him to it. As soon as I gave it to him, those fingers became immediately busy.