Backing Plate Differences

SBP 7 1/4 has a smaller diameter center hole, bearing is smaller, than 8 3/4

In the last 3 years someone posted a photo of a SBP, 7 1/4, 10 x1 3/4 backing plate next to a SBP, 8 3/4, 10 x 1 3/4 backing plate, center home was different.