Hi King,

I to cant wait to have ago at a project like this, you can get radial bearings with an ID for 8mm i question how well the fit would be though on threaded rod. Do you have access to a lathe, i'm thinking you would be better off turning down some plain bar to a tight fit, then you could also flange one side to match the inner ring of the bearing, you could then use another ring on the other side of the bearing with a grub screw to lock it off.

Its abit tricky not knowing what you want to do with the bearing so i'm only guessing its to fix the center studd for the cog's ?

.Me