I think there’s basically the following variations of A-C lengths (feel free to add/correct):
Original Yo around 390mm, pre suspension era
The 1” legged Yo that came on the 10th Anniversary Fat in 1992 that I think was still 390mm
The BOI officially introduced in 1993, with short suspension travel correction for early ~2” travel forks, around 405mm long
A few rare “proper” Yo forks with short sus correction, ~405mm like the 1993 BOI above but with the burlier 1-1/8” legs… very rare as most Yo’s were being fitted with suspension in 1993/1994, and at this point the BOI was becoming the only rigid fork
Some later (maybe 1996 ish?), slightly longer BOI forks at about 410mm? To cater for ~2.5” travel frames?
And the last edition of the longest 420mm BOI forks for the last NY era frames which had geometry for slightly more suspension (circa 3”) again.
Original Yo around 390mm, pre suspension era
The 1” legged Yo that came on the 10th Anniversary Fat in 1992 that I think was still 390mm
The BOI officially introduced in 1993, with short suspension travel correction for early ~2” travel forks, around 405mm long
A few rare “proper” Yo forks with short sus correction, ~405mm like the 1993 BOI above but with the burlier 1-1/8” legs… very rare as most Yo’s were being fitted with suspension in 1993/1994, and at this point the BOI was becoming the only rigid fork
Some later (maybe 1996 ish?), slightly longer BOI forks at about 410mm? To cater for ~2.5” travel frames?
And the last edition of the longest 420mm BOI forks for the last NY era frames which had geometry for slightly more suspension (circa 3”) again.
