Hi John,
Hi All,
the profile that our friends at Tru-Turn call "FAI" was intended to preserve the look of a 2-1/4" FOX "conical" spinner.
It seemed that nearly every fiberglass fuselage plug for those kits popular at the time (early 80's) was carved to match that same FOX spinner.
It was clearly lighter and better balanced than anything else on the market at the time.
So what was Bob Obenberger supposed to call it? Sorta-like-a-FOX? I think not.
The FAI Pattern guys asked for it, so that's what he called it.
At the time (back when engine displacement was the "real" limit) length was immaterial.

So endeth the history lesson.
take care,
Dean Pappas