8f.7 Ball Bearing Grades

      Harry Phinney <harry@hpcvlx.cv.hp.com>

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.

Good sources for ball bearings:

   Your local bike shop (make sure you're getting the grade you want)
   Bike Parts Pacific
   Bike Nashbar  1-800-NASHBAR    ($1-$3 per 100 Grade 25)
   The Third Hand 1-916-926-2600  ($4-$7 per 100 Grade 25)