This cast iron Primus No.1653 is a simmer plate which was manufactured in the late 1930’s. The underside of the simmer plate has three small ‘locating legs’. In the following picture, the simmer plate legs ‘butt up to’ the three leg support sections of the trivet (in this case, from a Primus No.50). Courtesy of @Spiritburner: 1937 Primus Catalogue No:6669 - Link | Classic Camp Stoves Translated… Pharael.
A really great, rare find! It's very easy to overlook this small item in the catalog. I overlooked it myself, even though I'd gone through the catalog several times Thanks for sharing .
