penny

A measure of the size of nails, at least as early as the fifteeenth century – 21st century. Symbol, d. The symbol comes from the Latin denarius through the French denier, and is also the symbol for the monetary penny. There are 240 pennies to the pound sterling.

In current usage, a 2d nail is 1 inch long. Each 1d increase is a ¼ inch increase in length up to 12d. A sixteen-penny nail is a ¼ inch longer than 12d, and the remaining sizes, beginning with 20d, are multiples of 10 and are each ½ inch longer than the preceding size.

illustration of nail lengths

The penny size was originally the price in pennies of 100 nails of that size. The hundred was the great hundred, 120, not 100. However, the penny system had already become purely conventional a hundred years before Queen Elizabeth's time, because we find in merchants' books entries like 100 4d nails for 3 pence, 300 3d nails for 7½ pence, and so on. “By 1573 'sixpenny nail' sold in fact for 3½d per hundred.”¹

The size is not based on the nail’s weight in pennyweights.

Another theory sometimes met with² is that the pound was once abbreviated “d” and the “d” size of a nail was the weight in pounds of 1000 nails; that is, a thousand 2d nails would weigh 2 pounds. Confusion between “d” for penny and “d” for pound did the rest. This theory is highly unlikely. R. E. Zupko, who made an extensive study of records of British weights and measures, makes no mention of “d” as an abbreviation for the pound.

1. Alison Hanham.
The Celys and their World. An English Merchant Family of the fifteenth century.
Cambridge (UK): Cambridge University Press, 2008.

Page 331.

2. American Electrician's Handbook, 12th ed.

Page 4-185.

Sources

Nayles called grett naylles that ys to saye iiii d. naylle v d. naylles and vi d. naylles the b...xl s.

Nails called great nails, that is to say 4 penny nails, 5 penny nails and 6 penny nails, the barrel.....40 shillings. [customs duty]

From a 1702 copy (British Museum Add. Roll, 16577) of a manuscript internally dated 15 July 1507, consisting of a list of customs duties on various articles, as reproduced as Appendix C in Norman Scott Brien Gras, The Early English Customs System, Cambridge (MA): Harvard University Press, 1918, page 701.