I'm in the midst of building my prusa now that I have all the parts printed. I'm in the USA so metric sizes are tough to get ahold of. I found some precision ground 8mm smooth rod from McMaster-Carr.
Product Number 5544T27 on page: [
www.mcmaster.com]
I believe this should work? Thoughts? Plan on using lm8uu bearings which is the main reason to use 8mm instead of 5/16.