Brass isn't a good material for such a shim, its too slippery. I sucessfully used shimmed a set of north road bars used upside down as cheapo moustaches. Pop can is way too thin for this application. I made my shim from a piece of flat aluminum stock that I found lying around work that I measured with calipers to confirm the right thickness. Never had any problems with it not holding in all the time it took me to decide I didn't like the bars. I think I roughened the surfaces with sandpaper, in a direction that would be parallel to the bars, but I suspect it made no difference.