I'll put the callipers on the bearings and let you know the size's...Its a very simple handle to maintain - Due to its design its actually difficulty to recognize when the bearing has failed due to its close tolerence on the shaft.
This is a pic of one I did the other day, water gets in primarily through the cap and then sits in there slowly corroding the bearing. As you can see to the point where the retainer has come off and the actual balls come out.
This is probably the 3rd or 4th one that I have seen like this...Removing the inner parts of the bearing is easy, the main problem is removing the outer ring which by now has corroded and stuck fast to the knob, had to dremel this one out.
I would suggest when NEW, that you dissasemble the knob by removing the top cap and remove the screw as seen in the pic - this will allow you to remove the knob from the shaft, coat the shaft with grease and replace the knob. Once that is done simply add grease to the inside of the knob and the top of the screw head..put as much as you want. Finally add grease to the thread of the cap to provide a better seal.
Every now and then just remove the cap and check its all ok...The flatter knob they sell has less issues.