Good point Tuck..
I was reffering to actuall PHYSICAL design differance..
On Keihin branded jets, there is a Taper at the bottom of the threads (base) that seats into the carb..
On the AB ones I have... it is Straight cut.. and never feels like it bottoms in the carb... Just when it feels like ti does, the threads bust.. (I have never busted main jet's before I bought these ones)...
Also the external dimentions are the same... except for that taper, which on the AB jet.. is taller..