In the 1960s I purchased a Rohm (German) 4 jaw self centering chuck and over the years have found this so convenient as it will accurately hold both square and round stock, why are these 4 jaw chucks so scarce as to me they are so much better? Don't know if they are still available, I don't think the extra jaw would put the price out of bounds.
This chuck of mine has been in constant use and still runs to a couple of thou. if I were starting a home shop again I would definately invest in another. David