I am off learning and teaching at Marc Adams School of Wood Working, expect shipping delays for next 2 weeks..
These are the bearings that match the ones used in my Custom router bit. If your bearings are noisy or starting to burn the wood they need to be replaced. The most common source of problem is excess pressure on the guide bearings when cut the net groove. Gentle pressure and a slow feed rate are all that is necessary to cut a uniform groove.
One more point, it is really hard to know the quality of the bearings that I get as a small supplier, so I can make no claims about quality. The bearings in the past were marked with the county of origin but it is no longer a uniform standard.
If you can source locally, bearings made in the USA or Japan, they maybe more consistent, but pricey. I have used these bearings in my shop for years, but one batch to the next can be a problem.
The pricing is for a set of 2 bearing.