I've never found a definitive answer as to what they were used for, but there is an interesting paragraph in the 1869 book by George Frederick Ansell, published in 1870, who worked in The Royal Mint at that time. He says: "For the past four of five years the reverse die has been made to carry, in addition to its recognised device, a small number, with a view to determine at which coining press, and on what particular day, the numbered die was used, that bad work might be traced to an individual. It need hardly be said that accidents encountered in daily work entirely overcome the object being sought, for a die may last either minutes or days in wear owing to the irregularities of the steel from which it is made, and besides, the boys who work the presses are of necessity changed at irregular intervals." Hi Nick, Thanks for the interesting information. So the Royal Mint were possibly looking at ways to keep tabs on their staff and equipment - a sort of quality control on their coins. I shall certainly have fun attempting to collect all the variations now. :-) D