No, it is not Hex, it is Hvy (Heavy) - judging by comparison with other records that appears to mean the roughest linen finish available (so they didnt fall over I guess). I don't think it had anything to do with weight.
Very interesting looking through all these chipcos that in the early days there were more distinct finishes than we credit chipco for.
Definitely a very rough linen and a not so rough. The satin type finish was not as smooth as the more modern, and then there was the finish like glass.