The claw hammer is used for driving nails. The claw end is used for removing nails. A hammer is sized by the weight of the head. The most common sizes are 13 or 16 ounce. You should use an appropriate hammer for the size of the work you are doing. A heavier hammer will be better for driving large nails, while a small hammer is better for small finish nails. If you use a large hammer to drive small nails, more than likely you will bend the nail or smash your finger.