  Diamond grinding wheel. 
Very attractive diamond-studded grinding wheel. The industrial-grade diamonds are embedded in a matrix of relatively soft iron, I'm pretty sure the bronze color is a plating, but it's too pretty to use and find out. 
The gaps are to allow the chips to escape, and possibly for cooling as well. 
Source: Harbor Freight Tool Company 
Contributor: Theodore Gray 
Acquired: 11 March, 2009 
Text Updated: 12 March, 2009 
Price: $25 
Size: 5" 
Purity: <2%
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