Lookin' at Oakeshott's sword typology right now and trying to pick out the best fit for the master-sword. I've found several hexagonal cross-sectioned hand and a halfs of varying proportion, but most lack a ricasso.
XVIIIb is diamond cross sectioned, but would fit the sword's proportion and purpose nicely.
XX/XXa both work nicely as well. XXa is even hexagonally cross sectioned.
Add a ricasso to XXa, and you pretty much have it.