@Gene2308: Why "sterile"? Are you afraid you'll get the balls infected?
Loose balls are very cheap if you buy them in bulk. Even the somewhat-overkill
grade 25 stainless ones are less than $0.10 each if you buy them in bulk. The normal
grade 25 through-hardened steel ones are even cheaper. Thus, there's no need to go through the trouble of cleaning them, especially since you'll need to make sure they're rinsed properly before popping them back. That's a lot of trouble when you don't even know if the balls are still within tolerance.
In any case, if you plan on doing this regularly and have a bunch of hubs that use the same size balls, it pays to keep a stash of new loose balls handy. For example, Shimano fronts tend to use 3/16" balls and their rears tend to use 1/4" balls, regardless of model; recent loose-ball Campagnolo hubs, front and rear both use 5/32" balls. With a selection of three sizes costing me about $150 (for stainless ones), I've got a lifetime supply for all my hubs.
Here's an interesting
discourse by
bimini from
RoadBikeReview Forums regarding this very subject. The whole thread is
here.
Finally a subject that I am a true expert on. I worked as the plant engineer for 5 years at the largest ball bearing factory in the US. We made a million pounds of balls a month. (Thats a lot of balls! as we use to say)
In the higher tollerance bearings, grade 200 and better, matching lots is manditory. The ball to ball tollerance within a lot of grade 25 balls is 0.000025" however the balls can very from the listed nominal size by as much as 0.0001". All balls used in a bearing race must be changed when replacing balls, and all the balls used must come from the same lot. Otherwise you will have balls of different sizes in the bearing and all the load will go on the biggest ball, overloading the ball and the race.
Grade 25 is really an overkill for any bicycle application. But for the few pennies more they don't hurt. I am sure campy uses the 25's just because they feel smoother when spinning the hub by hand. (the look and feel of things are very important to the Italians) You don't have to have grade 25s until you start seeing 5000 RPM's or more, and this is only due to the heat buildup of rougher bearings at those speeds. Grade 10s are only needed in very high speed racing engines and such. We also made a few grade 3's that were used in jet turbine applications at 30,000 to 60,000 RPMs. Those bearings got real pricey, just measuring something within 0.000003 inches tooks some very special and expensive equipment.
Using too smooth of ball can cause lubrication problems. If the ball is too smooth it will not carry the oil or grease around as it rotates. Grade 10 may be a bad choice depending on the type of lubricant being used. For grades lower than 25 the finishing process of the balls change. Grade 200 to 25 have a ground finish and do a good job carrying oils and lubes. Grades 10 and below have a lapped and polished finish and are normally used only in pressurized lubrication systems where oil is constantly forced around the bearings.