What are the different grades of ball bearings?
From: Bill Codding , Harry Phinney
Following is a description of the different grades of ball bearings. The
grade specifies the sphericity of the balls in millionths of an inch. Thus,
grade 25 are round to 25/10^6, while grade 1000 are good to 1/1000 (i.e.
not all that round, but probably good enough for our uses).
Grade 25: the highest quality normally available, aka "Campagnolo quality":
hardened all the way through, best alloys, coatings, roundness, and durability.
Evidently, a recent bottom-bracket overhaul article in "Bicycling Plus
Mountain Bike" magazine recommended these. Campy's tech reps claim that
the bearings in a set (usually in a little paper bag) are matched. One
should not mix bearings from different sets.
Grade 200: mid-range
Grade 1000: seems to be the lowest, may only be surface hardened.
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