It's just a solenoid. Electromagnet pulls one way, spring pulls the other.Warning: Trying to do this thing without adequate sterilization is a good way to get sick. Trying to do it without understanding the behavior of the inks over time is a good way to wind up with lousy tattoos, and they're REALLY unpleasant to remove. Seriously, this is not something I would recommend trying to homebrew.If you're just trying to tattoo numbers in calves ears... MAYBE. Though I think the SPCA would be likely to get on your case, and the FDA might also.