Salvador,
You can use a couple of steel washers to take up the space in the arbor hole or you can stick them on the end of the arbor (ugly!!) . The main points in doing this is to be able to install the wedge correctly (a good smacking! No "finger tight" junk!), so that you will remove all the arbor/arbor hole/ frame fit clearances and have the same barrel/ cyl clearance each time you assemble the revolver.
Smacking in the wedge also applies "tension" to the assemblies and allows the forces from shooting to move through the revolver as one solid unit. That's what keeps the two assemblies from beating the wedge up.
Also, I find the "fix" for the Uberti's and the Piettas to be about the same. Even though the arbor is sorta correct in the Piettas (at least you can install the wedge correctly!!) it's too long for my tuning service. I still have to dress the arbor down to end up with a .002"min.- .003" max. barrel/cyl clearance. The extra cost of the Uberti is reflected in the action parts. The parts today are very nice and much easier to set up. Piettas on the other hand have parts that are every bit as good as 1970's vintage!! Lots of "massaging" to get them right. So, it's a fairly even offering as far as work time with either.
The Uberti is a perfect platform for a really excellent revolver with more correct lines/ sizes and with at least the same time (and many times more time) the Pietta can be as excellent.
The decision of "which to get" can also be dependant on if a cartridge conversion is in the future. The longer Pietta cylinder is nice because it will accept factory length ammo whereas the shorter Uberti cyls usually require deeper seated bullets. (This pertains to .44 cal./.45C revolvers of the '51/ '60 variety). Wow!! lots of decisions to make!! Just get one of each!!
Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks
Sorry Hawg, didn't mean to answer for ya! I'm a s-l-o-w typer apparently!!! Lol