An attachment is retrofittably attachable (and detachable) to a conventional hammer to render the hammer head magnetic for purposes of starting a metallic fastener such as a nail. The attachment includes a cup-like housing within which is disposed a magnetic unit that includes at least one magnet. One surface of the magnetic unit magnetically attaches the unit to the striking surface of the hammer head. The head of a metallic fastener is magnetically attachable to the other surface of the magnetic unit.