The mid-70's "Shimano 600" parts eventually became the "6xxx" series of components, and the Dura-Ace / Crane components became "7xxx" which means Dura Ace might have originally been considered "Shimano 700" components. Was there ever any reference to "Shimano 700" components in Shimano's literature?
Shimano 105 is the third level stuff, but in this case I think it's a marketing name and they put the '5' at the end of the name on a whim, because the parts numbering series is '5xxx', so Shimano 105 is really Shimano 500, in the catalogs.
Anyway, this reminded me that Atom/Maillard offered 600 and 700 and 500 series components, but the best stuff was Atom 700 (e.g. the pedals) and Maillard 700 (e.g. the hubs.)
So did Shimano plagiarize the Atom/Maillard parts numbering scheme? It seems likely. I'm surprised they didn't make Dura Ace Shimano 8xxx because 8's are really, really lucky in asian culture.
- Don Gillies
San Diego, CA, USA