  Tungsten spark plug. 
Or at least, a spark plug made by a company called Tungsten.  I don't really know if there is any tungsten in any part of these spark plugs, but I'll eventually test them and report what I find. 
The most interesting thing about this sample is that not just one but two people would be willing to pay a minimum of $40 for a single rusty old spark plug (it takes two people to drive the price of an auction up).  I'm not sure why I was willing to bid that high, and I certainly have no idea why the other idiot was, but isn't it wonderful that eBay exists to allow the exchange of a million people's junk into a million other people's treasure! 
Here's an  interesting article about different elements in spark plugs. 
Source: eBay seller foos15 
Contributor: Theodore Gray 
Acquired: 12 November, 2002 
Text Updated: 29 January, 2009 
Price: $41 
Size: 4" 
Purity: 0% 
Sample Group: Spark Plugs
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