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The increase to 4.5 mm balls on the bottom race /crown race is an old trick so the balls can't sit in the dents so headset gets to survive longer
A 4.5mm ball in a 5/32" dent just sits on the rim with a high pressure curved line contact. It rolls through the dent better than as 5/32" ball at first, but the extreme contact pressure just means you very quickly have a 4.5mm dent. A 4.5mm ball is sufficiently oversize compared with 5/32" that it's bigger than the raceway curvature in typical bearing designs, which isn't a good place to be.
gbj_tester-
Now this is the third time that I'm writing this. Now feels like the web hates me.
This is a lower races and are already on the way out. The bigger ball bearings give it longer life. This races are not that precision machined. Have you ever checked the curvature of the races? Checked the relation to the race to the top of the mount.
These things aren't precision made so wouldn't worry about something that isn't rotating just occasionally wiggling.
lynx
Thank for correcting my spelling error.
The taken as read is the change to loose bearings hence asking the grade, as caged bearings don't come with a grade listed on packets I have seen.
The increase to 4.5 mm balls on the bottom race /crown race is an old trick so the balls can't sit in the dents so headset gets to survive longer. With the same size balls, the balls can still go in to the dents made in the races.you just hope by adding more that dents no longer match up.
We could go and discuss if you should use chrome or stainless steel but each has advantages and draw backs. Are chromed steel bouncier, does stainless wear more? You decide.
All I say is use an automotive marine wheel bearing grease. Helps the grease say where it is supposed to be.