Maybe the date isn't absolutely certain, but according to the anniversary book from B.A.Hjorth, the early stoves without any name was made before Hjorth took over the sales in 1892 (The tank lid with the Hjorth name on it could of course be a later replacement in that case). This one is practically identical in the general features with the one I posted here. The only differences I can notice (on things that couldn't have been swapped through the years) is that they actually folded the rim from the side of the tank around the bottom plate on this one in contrast to the other one. The other difference is that there is a little rivet looking thing at the very centre of the bottom, and that there is the letter "P" stamped in it just beside that "rivet". The burner has obviously been changed, and this one is also missing the top lid (If anyone has that part, I'd be interested in it). The tank lid has the text B. A. Hjorth & Co on it, and the patent number 6186. Saying B.A. Hjorth should mean at least after May (I think) 1892, but the lid is not something you should use for dating an item. Only indicating. The patent number is either mis-stamped (it is so on another old Primus lid I have) or referring to another country than the usual ones. I have tried all those who BAHCO exported to in the early stages, and no one is correct. E.g. the Swedish patent for this number is about a three-sided nail... I would assume that the folded rim is an improvement from the other old stove from this pioneer era, so I think this one is slightly newer than the other one I posted. The text on the pump lid is correct for the period according to the Anniversary book from B.A. Hjorth. It also show a lovely amount of wear. This stove has surely been used! The pump tube is surprisingly un-damaged. Generally someone has used a pair of pliers to remove it at some time on these, but this one has obviously been removed with the correct tool all time. And it came out pretty easily, showing the usual pre-1896 NRV. The valve is still working without any flaws! The old cork is sealing, and the spring is still springy. The old pump leather was also working satisfactory after three days in mineral oil. It's wonderful to see a 120 year old item still work as intended. I have pressurised it as it came, using the old pump leather, old cork NRV and even with the old cork in the tank lid, so I have no doubts that it will work once I'll find- or make - a new lid for that burner. That's a winning concept to you.