I'm kinda thinking this is splitting hairs, 1/16" gap on that assembly should be no big deal, it doesn't bind up at least... if the slop is a big downer, simply find a thin rubber o-ring of the correct diameter, and slip it in there.... pretty simple. No?
As noted I'm sure the casting dimensions can vary a bit...
Or, as mentioned, super thin wave washers, which have been used as OEM parts on many bike pegs from the factory, work well...
They are cheap also...
http://www.mcmaster.com/#standard-washers/=wmzr5d