the SRW F-350 has a heavier duty rear axle under it compared to the F-250.

 

I thought that all SRW Super Duties had the Sterling 10.5.

 

I'm not sure of all the details but the one ton has a 37 spline axle shaft with different bearings whereas the f250 has a 35 spline.

 

I can't remember reading about anyone that actually had the 37-spline shafts, but the F350 is supposed to have Sterling 10.5 with 37-spline shafts and the F250 is supposed to have the Sterling 10.5 with 35-spline shafts. I can't find anyone to confirm it though and some with a F350 have 35-spline shafts, so I'm not sure if it ever was a real difference.