Here's my example of this coin type: It's from Hungary, struck by the king Bela III (1172- 1196). Obverse shows Bela and his brother Stephen enthroned, reverse shows the Virgin Mary.
I don't have a scale handy, but the diameter of my coin is 28 mm. It is very thin, and I believe it may have originally been slightly scyphate (cup-shaped) and then someone tried to flatten it out, creating the large cuts in the flan.