I was just hanging my spools on the rod of my k8200 as i suspect most do, initially anyway.
It rattled abit and jerked which i'm sure isn't a positive on accuracy.
I got bearings for pence from the far east.
http://www.amazon.co.uk/gp/product/B0056EVJX2?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
6mm ID would be better, but it matters not for this part.
Now it rolls lovely.
Plus now i have a spare penny washer and lock nut.

When produced, sand/file the bearing space. put the bearings in the freezer, heat the part to a 100'C and after a few minutes itll be ready for a press fit using a vice or bearing puller. Same for the nut handle.