What is this bump on my thumb? (Photos)

I have had this "growth" on the side of my thumb knuckle for a few years now. It is a raised bump with a flat surface. It doesn't hurt, aside from overuse in that area. It doesn't necessarily fit any description of warts, so I'm not sure what it could be. I've tried wart remover band aids and it will turn white and flake off a bit, but always comes back same as before.

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