Missile part. 
This is a machined beryllium missile part of some sort.  Beryllium is extremely toxic in powdered form, but relatively harmless as long as it's fully intact.  Making a part like this must be quite difficult to do safely considering the amount of very toxic beryllium dust and shavings that would be generated. 
Source: eBay seller parker282828 
Contributor: Theodore Gray 
Acquired: 12 May, 2004 
Text Updated: 18 October, 2009 
Price: $67 
Size: 1.25" 
Purity: 99%
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