a tool that fits on the exposed head of a nail

A pointed tool with one round or square end, used to drive nails below surface level.

This steel punch has a tapered flattened end. Driven with a hammer, it sets the heads of finishing nails below the surface of the wood. Home Improvement Encyclopedia

Finished and fine woodwork require that nails be set or sunk slightly below the surface of the workpiece. A hammer and a nail set recess the nail, allowing the remaining cavity to be filled and blended with the surrounding wood.

A small hand tool, like a punch, used for setting finish nails slightly below the surface of the wood.