Re: roller bearings *LINK*

5x9's are still in the AAR manual, but during a project building new equipment using roller bearings a few years ago, Rocky at ORX advised us to not use them since they are so rare. While they might be (just barely) available now, they are on the way out, and replacements may become impossible to find at any time.
The larger sizes are easy enough to design new trucks around, but with existing narrow gage trucks, the modifications needed would be too great to be practical.
I don't see the need to convert existing equipment in the first place, since in 26 years of steam railroading I have yet to come across a hot box on a regularly used passenger car, but maybe I'm just spoiled by conscientious car men.