8 3/4 Rear Axle Tube Diameter

My rear is from a ford explorer, the tubes are 3 1/4 dia. I used the 8 3/4 shock mount plates on it with no modification. Just kind of squeezed the u bolts in when I installed them. Or are you talking about spring mount perches? I had to use 3" dia, and grind them to fit using an angle grinder.