The Cona brew board listings on the CoffeeBOS shop on Etsy use a Model C brewer as a frame of reference. That’s because the Model C/D brewers, which are still in production today, share a common base. While vintage Model A or B brewers have a smaller base, all four models share the same spirit lamp. So the diameter of the hole in the base is consistent across Cona Models A through D.
As shown in this photo, Model A and B table top models are compatible with CoffeeBOS brew boards for Cona vacuum coffee makers. Since Model A and B brewers have a smaller footprint, that leaves more of the brew board exposed for you to appreciate!