Randy
Have seen the different part numbers associated with the different carrier bearings and did not fully understand why they were different. So although internally, the 28 and 31 spline carriers are the same, the outer bearing on a 31 spline carrier has larger dimension which would require smaller (slim line) bearing for use in a 28 spline case. Normal outer bearing if used in a 31 spline carrier, slim line used in 28 spline carrier.