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3D2 inch anode ball.
Purchased from eBay seller "El_Three" in May 2002. Similar balls are for sale in 100lb quantities by suppliers who list them as "anode balls". I'm not clear what industrial process they are used for, but reader Dan Burrill from the UK reports as follows:
It is almost certainly used in electroplating, where the anode often consists of a cloth bag containing balls of metal or shot, depending upon the exact coating required. I'm not an expert on the subject, but my late father and I have worked in plating factories in the past and seen this in action. I believe this is done to provide a larger surface area, whilst the cloth bag prevents particles of the disintegrating anode from detaching and adhering to the article being plated.
From memory, nickel-cadmium plating used to be used on engine parts and other high-wear, high-temperature items, but I know this was banned in the UK some time ago (I'm not sure about its current status in other parts of the world). I believe it was replaced with zinc-nickel, but couldn't say for sure.
Sounds plausible to me.
Source: eBay seller el_three
Contributor: Theodore Gray
Acquired: 13 May, 2002
Price: $35
Size: 2"
Purity: >95%