Q From Richard Bell: Why is the length of a nail indicated by a number of pennies? (I don’t know if this is the usage in the UK, but in the US nails are always measured this way.) A 6d nail is 2 inches long, for example. I have read that this is because, at one time, sixpence was the price of a hundred 6d nails.
A We did once use the same system in the UK — it was invented here and taken to the US by colonists — but it died out early in the twentieth century. Not only have we gone over to measuring nails by length but we’ve adopted the metric system. So an American 6d nail is a 50mm one. As in other matters, the US conservatively holds on to things we’ve abandoned in Britain.
Many enquirers have found the story you quote to be unbelievable and have sought others. One holds that nails were actually sold by weight and that the measure was the pennyweight; the abbreviation for a pennyweight was dwt (the d is from Latin denarius, a penny) and it is argued that this became shortened still further to d, which was the symbol for the British pre-decimalisation penny coin, hence the confusion.
A second suggestion was put forward here and has been quoted since:
The term penny, when used to mark the size of nails, is supposed to be a corruption of pound. Thus, a four-penny nail was such that 1000 of them weighed 4 lbs., a ten-penny such that 1000 weighed 10 lbs.
The American Cyclopaedia, edited by George Ripley and Charles Dana, 1875.
With Ripley, you may believe it or not, but you had best not. Neither the pound nor pennyweight stories are right. Yours is.
In the fifteenth century, nails were sold by number and, for example, fourpenny nails were indeed 4 pence for a hundred. This was proved when in 1904 Henry Littlehales edited and published the accounts of a church in the City of London (St Mary at Hill). This showed that in 1426, 400 sixpenny nails did indeed cost 24 pence and 300 tenpenny nails cost 30 pence. (You may like to compare these prices with a nearby item which recorded that a man named Elymesford and his mate were together paid 10 pence for a day’s work.) Other accounts show that nail prices fell around the end of the 1400s and stayed lower — in the 1570s, you could have bought a hundred fourpenny nails for just 3 pence.
However, the old names for the sizes were kept. Although they lost their direct equivalence to the cost of the nails, they remained a useful way of identifying the various sizes.