Primus paraffin stoves, lanterns and blow lamps (blowtorches) are stamped with a letter code starting in 1911. The letter code can be found on the bottom of the tanks of these liquid fuel pressure appliances. The letters Q and AQ are not used in the coding system. Starting in 1955, the code method changed and a six-digit code was used. The last two digits of the six-digit code correspond to the year of production. The six-digit code can often be found on the leg of the stove or on the burner riser of the stove. Toward the end of the last years of Primus production, the code was no longer stamped on the stove but was found on the carton the stove shipped in.
There is often an additional number or letter stamped on the tank. It is unclear what this was for, but it is possible it was a production line identifier, or lot batch number.
Primus is the only liquid-fueled pressure appliance company of which I am aware that dated their offerings with a date code. Other manufacturers appliances must be dated by examining the features of the appliance and comparing them to catalog drawings, photos, illustrations and known dated appliances of the type.
You are welcome to freely copy and distribute this dating chart, link to the dating chart, or link to this webpage. Click on the chart or the photos below for larger and higher resolution images. While I made this chart from scratch, I am not the originator of the chart. For the record, I only published my homemade chart here after I saw that the original chart (found on a popular and well-known social discussion forum requiring a membership and/or subscription fee) has been published in full resolution far and wide all over Pinterest. So, the horse has already escaped the barn. I do not believe knowledge should be held ransom behind a subscription fee. Apparently a lot of Pinterest users agree, and you should agree, too. 👍
Here are some examples: