Finishing nails are small nails with very small heads. They are usually used for "final touches" such as molding or trim. They usually are sunken into the surface and leave a small hole that can be filled in with putty and painted over for a smooth finish and invisible nail and nail hole.
Finishing nails are made of steel, and they come in different sizes and thicknesses. The gauge size, or thickness of the nail, is a measure of how strong the nail is. Gauge size ranges from 16 to 10, the smaller the gauge size, the stronger the nail. Finishing nails vary in length from 1 inch to 4 inches (2.5 centimeter to 10 centimeters). The size of finish nails is also measured by "penny" units. The letter "d" is used to determine length. In this method, a 2d finishing nail is 1 inch (2.5 centimeters) long, and a 6d nail is 2 inches (5 centimeters) long.