There was a post real early in the thread showing the differences in the knuckles big vs bigger, and caliper bolt spacing was one of them.
the 1550s fit either knuckle
Probably only got a normal 05+ axle
Look on the napa website, they always used to list important info like the bolt spacing on caliper brackets.
Rock auto may list detailed data it that helps?
My axle is this...actual picfwiw in 2013 the 250 and 350 went from 13.5ish to 14.5ish rotors
2008-2012 450 factory pickups had smaller brakes than 450/550 cab and chassis did
I don't know the exact year and if there were number on the housing they are long gone because I cut it down for a rear steer axle...
I bought 04-f450 rotors and f550 calipers as per this article
Dana Super 60 High Pinion Front Axle - 4-Wheel & Off-Road Magazine
2004 f450 rotors fit no issues(14.5 OD rotors) mounting bracket spacing is a lot wider than the actual 8.5" on the knuckles
After some research(mostly looking at different year pics on oreillys website) the 05-09 calipers have the big 10.75" mount spacing. Now the 10-12 "appears" to be a lot closer spacing and the 13-up Looks the same way but calipers look like a different shape
Im gonna stop by the parts store and have them pull both the 10-up and 13-up calipers to measure....
Where is Billavista to write an indepth article on these???..... this thread is too deep with few facts that aren't 25 pages apart.....