What's a "Fat Font" typography

The term Flat Four (or Fat Four) appears on a specific version of a Rolex watch: the Submariner 16610LV MK1. This version of the Submariner, also known as the "Kermit" – and not the "Hulk" – was released in 2003 to mark the 50th anniversary of the Submariner. In this version, the font used for the number 4 is flatter, hence the term "Flat Four," characterized by a flat section at the top of the numeral. There are two types of insert typographies associated with the Flat Four. The first, "B1," features serifs, while the second lacks them. According to observations by collectors, the B2 bezel (without serifs) appears to be a replacement bezel used by Rolex between 2003 and 2004.