Keep in mind, what you’re calling a “G2” in your pic, Briley calls a 3rd Generation on their website. They call the chokes with the threads at the top (found in most MT6s and some TM1s) a 2nd Generation:
Your G3 looks kind of like a flush version of the G2. Are the thread pitch and/or bore sizes different?Yes.
There's one problem, if Briley call this G3, then there should be 5 generations of P chokes. But they only listed 4, they missed one generation between their G3 & G4.
Look at my picture, they missed the G3 in my picture, based on their categorization, their G4 should be G5.