Mk10+ Yoke to DIN

[Zung]

I agree: I've nothing but contempt for fractions.
That being said, it's logical: the 26 mm is for Aqualung, a (mostly) French company.

 

[DA Aquamaster]

If you are just removing the yoke retainer nut, a BACW (big assed cresent wrench) will work fine, provided the nut is not over torqued or corroded in place. A 15" wrench works pretty well if you have one or can borrow one.

A suitably long reached 6mm allen head socket and torque wrench are the tools of choice for installing the new DIN retainer.