Originally Posted by
70sSanO
Interesting question. The 6402 freehub is UG and HG.
IIRC, the interesting part is Shimano made a Dura Ace UG 8 speed cassette, but the 1st position threaded cog was not compatible with non-Dura Ace UG freehubs. I don’t recall a Shimano 600 UG 8 speed cassette, but they may have offered one.
John
Shimano offered 2 DA 8 speed freehubs, the first was UG with the DA smaller thread diameter, so only DA cassettes. The second was UG/HG but with the larger thread diameter for UG cassettes with the larger thread diameter, so made to be backwards compatible with 7 speed non DA cassettes.
Don't recall any 8 speed UG cassettes for the Ultegra group, standard component for the group used a HG90-8 when the group went to 8 speed. MTB probably also was on HG when the groups went to 8 speed.