  Zirconium oxide flap disk. 
This is a sort of combination grinding wheel/sand paper used to do really rough grinding of welds.  The abrasive is zirconium oxide, basically industrial-grade cubic zicronia fake diamonds. 
Source: Harbor Freight Tool Company 
Contributor: Theodore Gray 
Acquired: 11 March, 2009 
Text Updated: 12 March, 2009 
Price: $8 
Size: 5" 
Purity: <30%
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