smontanaro 

I have three Dura-Ace MF-7400 freewheels, one which is six-speed and has a range which looks reasonable (24- or 26-T big cog, not in front of me ATM). Two are seven-speeds and more corncob-ish. I also have a MF-6208 six-speed, again with what I consider a reasonable range.

Before I attempt to get all Hulk-ish with my chain whips, is there any chance I can mix-n-match the cogs among these four freewheels to get one or even two wider range 7sp freewheels, or despite the part numbers are 6sp and 7sp MF-7400 cogs and bodies incompatible? (I'll worry about the 6208 later, if the 7400s turn out to be sympatico...)

cdmurphy

Yes, the 6 speed MF-6208 and MF-7400 are identical from a functional point of view. I think the cogs may have had a different (nicer) finish on the Dura Ace model, but they're the same beyond that. The 7 Speed MF-7400 is a bit different, as it lacks the dust seal on the outside face, and requires a unique 1st cog that screws into a unique 2nd cog. You can certainly mix and match between any of the MF-6208 and MF-7400 cogs (other than the 7s specific ones.)

smontanaro 

Cool, thanks. Now for a bit of calculation followed by a bit of wrenching.