Jill, I thought you might be interested in some other information about nails. Hope it gets you some extra credit.
The "penny" system for sizing nails originated in England. The letter "d" was the designation for the English penny. In the early days, the same abbreviation was used to indicate a pound in weight. Nails were weighed by the thousand, so if 1,000 nails totaled 2 pounds, they were 2d, or 2 penny nails. The penny system has endured, althoughtoday it refers only to nail length. For example, a 2d nail is 1 inch long. Each higher number represents an increase in length of 1/4 inch, up to 12d (3 1/4 inch long). After 12d, the penny system becomes more irregular. Today, there are approximately 890 2d common nails (big heads) or 1.380 finishing nails (small heads) per pound.