Wayne, check the postings for the past two weeks, one of which is a long thread re Mustad hooks in which Dr.Fish (Mustad Employee) explains the reasons for the switch.
It comes down to the Hooks before were named as close as possible to what they were but were named using old technology.
now with the upgrade using modern tooling, more consistent metal etc they are able to make them more consistent with in the series IE a 4x is 1/4 longer than a 3x and the hook gap goes up or down with the number. And they have upgraded there hooks descriptions to match.
Eric
"Complexity is easy; Simplicity is difficult."
Georgy Shragin
Designer of ppsh41 sub machine gun