FATBOY mouthpieces are fatter than the original Guardala’s. The elliptical shape allows the mouthpiece to have a larger size, with a lesser increase of weight. The resulting size/weight ratio is the only way of producing a “BALANCED SOUND” with a mouthpiece larger than the original Dave Guardala Mouthpiece. (Original Chamber) 114 

Though the legendary Dave Guardala himself is no longer making mouthpieces his former workshop colleague, Nadir Ibrahimoglu of PMS music in Germany, continues to make and distribute these remarkable 'pieces. Guardala very much set the standard for the top quality, pro players' mouthpiece back in the 1980s- specifically his ground breaking work for Michael Brecker.

The Fat Boy models are exactly the same internally as the pre-existing models but contain more material on the outside of the mouthpiece thus giving extra weight and resistance to the sound (if that's what you're looking for)…hence the name FAT Boy.