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I have seen a lot of people putting the magnet on side of their ring finger on the pinky side of the hand, is there a reason you should go for this rather than the thumb side of your hand.
There are a lot of nerves in your fingertip
One possible reason is that the ring finger is substantially longer than the pinky, and would rub against it less, causing less irritation. The middle finger is typically longer than the ring, however, and would result in more contact and likely more irritation.
Going off of what misslitty said, the ring finger also tends not to have to deal with as much use as the index finger or thumb. This decreases chances of rejection, and can improve sensitivity in the long term.