Hi, I have been posting some photos of Primus No.4 stoves recently and have been giving some thought to the evolution of the silent burners on these stoves. Here are my preliminary findings: The Primus No.4 was introduced fairly early in the life of Primus stove manufacture, probably around the start of the 20th Century. The earliest silent burners had a deep "skirt" extending around the burner caps, and the outer "cap" had a fixed perforated screen brazed to the vaporisation chamber. This form of silent burner cap was replaced with the now more-familiar, removable inner and outer burner caps by the mid 1920s, although the deep skirt was retained. There is an example of a 1925 Primus No.4 with the fixed perforated screen outer cap on the CCS website. I have posted photos of a 1926 Primus 4 with a burner with the more modern removable inner and outer silent caps. Both these stoves have the deep skirts around the vaporisation chamber and burner caps. The next stage in the evolution of the silent burner used on Primus No.4 stoves seems to have taken place in 1935. The "skirt" became shallower although the rest of the burner remains as before. In the CCS Gallery there is a 1934 Primus no.4 with the deep skirt design, posted by mbechtel. I have posted images of 1935 and later No.4 stoves with shallow skirt burners. Here are some images to illustrate the two burner styles described above: On the left we have the "deep-skirt" form used up to and including 1934. On the right we have the later "shallow skirt" style used from 1936 until the end of production, probably in the late 1940s. Below we have two more detailed photos of the pre-1934 "deep-skirt" form of No.4 burner: Finally, two photos of the "shallow-skirt" No.4 burner used from 1935 until production ceased in the late 1940s. I look forward to receiving any comments. Best Regards, Kerophile.