Welcome to brain Stuff from how stuff works dot com, where smart happens the high on Marshall Brain with today's question, can you explain the diameter measurements used in nails? You can buy nails ranging from twopenny up to sixtypenny in the United States, represented as two D or sixty D, respectively. When you buy a twopenny nail, what you're buying is
a nail that is an inch long. A threepenny nail is an inch, and a quarter fourpenny is an inch and a half, and so on, increasing by quarter inches. That works up to a twelvepenny nail. So a twelvepenny nail is three and a quarter inches long, a sixteenpenny nail is three and a half inches long, a twenty penny is four inches, and after that there's the thirty, forty, fifty, and sixtypenny nails, each one a half inch longer than the last, So a sixty penny nail is six inches long.
Why is D used instead of P when talking about pennies and nails? For example, a two D nail is a twopenny nail. It probably comes from the Roman coin called the denarius. It's not clear that anyone knows where the penny designation comes from, though it might have indicated the cost of a hundred nails of a given size in the four hundreds, but who knows. For more on this and thousands of other topics, is it how stuff works dot com