Did You Know? - The "12d" (pronounced "twelve penny") on the label is a carryover from the Roman "denarius", which was a small silver coin.
The British renamed it the penny, but kept the "d" symbol.
At that time, it may have referred to the cost of the nails, but now it refers only to the length of the nail (which is repeated on the label, in this case, as 3-1/4").