Was 7 blade fan standard or optional?

[Henrius]

My 1972 Newport with a 400 and 1965 Fury III with a 383 both had 7 blade fans. Both threw blades and all I could find was 6 blade replacements.... until I FINALLY found one on E-Bay the other day.

Was the 7 blade part of a trailer-towing or hot weather option? Why are these so hard to find?

 

[polara66hardtop]

Blades differed a lot depending on Factory A/C,tow package or clutch fan, or not etc.