Looking at my Panny 20mm 1.7, the aperture ring is maybe 15mm, I won't go measure it, but it certainly isn't more than an inch no matter how you slice it.
On the other hand, some old primes my father has are slower than 1.7 but when wide open, it looks as if the entire 20mm Panny lens could go through their aperture ring.
Are there any correlations between aperture diameters and f-stop number?