The FB3 had an approximately one-third blade length sharpened clip, and fairly short integral guards. It is a great knife, with good balance and lots'a chop. Then Ernie met Bill Bagwell at one of the Riddle of Steel events. The FB4 reflects a lot of Bagwell's influence on Ernie, as well as the natural evolution of the design. The FB4 has a two-thirds blade-length sharpened clip and wider integral guards. Ernie also started lengthening his handles somewhat with the FB4. The combination of the longer handles and more double ground blade makes the FB4 balance perfectly. They are lightening quick. Also, about the time of the FB4, Ernie started offering A-2 as his standard steel.
Cheers,
Harv