extremechanical, I think they are somewhat more common on feedwater heaters. I don't have details to share, but the few I've seen are pretty rudimentary. A couple pieces of barstock, one for the roller, one for the axle, a couple of plates to connect to the bundle.
I have also seen these on some compressed gas coolers, most were as described above, however one particular job used stainless steel yoke rollers.
Never seen rollers on an average TEMA type exchanger.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand