If it is fingernails or toenails, this represents the inner self that extends on the outside of you. Inner strength, spiritual energy, protection, flexibility, feelings, expression, and the ability to defend oneself. If it is nails that you are hammering, it represents persistent hits that you have endured in your life that have left a mark mentally. Is someone holding power over you? Are you in a situation that feels binding or that you feel stuck inside? Do you feel forced in some way?
See Growing, Hands, Fingers, Toes, Body, Scratch, Hammer, Tools, Mental, Mind, Rust.