  Cobalt-steel milling bit. 
This is a lovely 1.5" diameter, 6-flute cobalt steel square end mill.  It would be used in a milling machine to cut a variety of metals.  I list it under cobalt even though the main ingredient is of course iron, because cobalt is the ingredient that distinguishes this alloy from other steel alloys with different properties.  Cobalt steel is particularly hard, and thus suitable for cutting tools. 
Source: eBay seller valpone 
Contributor: Theodore Gray 
Acquired: 9 February, 2009 
Text Updated: 8 February, 2009 
Price: $15 
Size: 1.5" 
Purity: <5%
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