I guess there are methods to get them off, but for the most part, they fall off by themselves going down the road, or they are put up QUITE the fight...
I just measured the shifter that is off of a M5OD-R2 (I belive, it might be an R1), and the diameter looks is over 1/2", but smaller than 9/16" 's, so I guess that would be 17/32".
If you are drilling your own hole, I would just drill it to 1/2" and just make it slightly bigger untill it fits.
Well, that took a couple minutes to type, but it took me a couple hours to hit the submit button...