I'm going to suggest that the diameter of the crash bar will be the least of your problems. Based on what I see with the OEM bars, the location where you would want to mount those pegs is not perpendicular to the bike. (if that makes sense)Is anybody using these AltRider highway pegs on their OEM crash bars? They claim they work on 7/8" crash bars.
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I have no need for a skid plate at the moment, but will go for the Happy Trails solution, just to use their highway peg bar if these are not a viable siolution.
The Altrider pegs only have two directions for adjustment. The main clamp will swivel 360 degrees around the bar and the footpeg itself will also swivel 360 degrees on the mount itself. No matter how you adjust those pegs they will always be perpendicular to the mounting point. You will need a third swivel point to level out the pegs.
Having said that, if I'm mistaken about the angles on the crash bars, everything I just said is crap!