Primus Dating Chart - From 1911 Primus paraffin stoves are stamped with a letter code. This is found under the tank. The codes Q & AQ are not used. From 1955 a six digit number was used, the last two digits corresponding to the year. This stamp is often found on the leg or burner riser tube depending on model. The code was also used on the petrol model No:71 but not from the first years of production. With regard to the later 6 digit date code it would appear that post-1964 the code may have been continued but stamped on the cardboard box rather than the stove. I have an unstamped Primus 5R with such a stamp on the box and the date corresponds to the date of the invoice which was with the stove. Many thanks to Peter Benscher, Bo Ryman, Dr.Peter Watchorn, Neil McRae & Arne Aasgaard for their assistance in compiling and updating this chart.