Can a front wheel have a different number of bearings on each side? I took my old, filthy bike apart to clean it up.  I have never done this before!

When I took the front wheel bearings out, I ended up retrieving 9 from one side and 10 from the other.

It seems like logically there are a few explanations:


There were actually 10 each side but I dropped one without noticing.
It's designed to have a different number on each side.
It's not designed to have a different number on each side, but the bike shop put it together wrong and I've somehow got away with it over the years.


I honestly think I was being super careful and that it's not (1), but I'm prepared to accept it could be that if the others are impossible!

And I guess in practical terms, what I really need to know is ... should I put it back together with 9 on one side, or should I buy some new bearings so I have 10 each side?  I think I read somewhere that 10 each side is standard for a front wheel.
It's not unusual for an asymmetric shaft (on some rear wheels or solid-crank bottom brackets, eg) to have different numbers of balls in one side vs the other. But it's a little unusual for a standard front hub.  And if there's intentionally a difference then there would be a small but visible difference in the size of the races as well.

Likely the hub was serviced in the past and one ball was lost (or you lost one somehow).  But it's not really terribly serious.  It's often recommended (as a general rule for ball bearings) to have "a full race minus one" vs having the race completely full, and your typical 10-ball bearing can survive reasonably missing 2-3 balls (though that's not ideal).

However, since you have things apart it would be worthwhile to replace the balls.  (Don't mix old and new balls.)  See if ten fit comfortably.  If they fit, and there's still room for a fingernail between them, then use ten, otherwise go with nine.