A narrow shank helps prevent splitting of hardwoods or of thin boards. Nails with a square shank are used to attach wood flooring to concrete. Most kinds of nails have a broad, flat head. A nail with a narrow head can be hidden in the wood by driving it completely below the surface with a punchlike tool called a nailset. The hole left by the nail can be filled with putty and then painted.
Roofers use a nail with an extra wide head to install shingles.
Upholsterers use tacks with decorative heads if the tacks can be seen. Sizes of nails. Nails that are shorter or longer than those are measured in inches or centimeters. The system of measuring nails in pennies probably began in England several hundred years ago. How nails are made.