Danny, I've used a 6" Blair as a daily driver for around 50 years, I can confirm the vice has a roller thrust bearing as I bought a six inch Blair for my son and replaced the bearing which was a common caged bearing used in tractor steering king pins. Find a picture of a 12 " please.
Danny, Iv'e had and used a 6" Blair double power for over 50 years, my every day vice, I restore full size steam engines, It is super tough, I would love to see or own a Paramo 12 " double power, to me that would be the holy grail of vices.