  Cubic boron nitride insert.
This very expensive ($70 list, $20 on eBay) milling bit insert is only about half an inch wide, but incredibly hard and long-wearing in applications involving continuous cutting of hardened steels (grade BNX20). For that price it better be!
It has a cubic boron nitride coating over a cemented tungsten carbide base.
Source: eBay seller cutting_edge _tool
Contributor: Theodore Gray
Acquired: 17 April, 2009
Text Updated: 17 April, 2009
Price: $20
Size: 0.6"
Purity: <10%
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