Tantalum Metal salesmans sample
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Metal salesmans sample.
From the eBay item description, which pretty much sums up what this item is:
This auction is for a very unusual, what I think would be called a Salesman Sample, of 5 exotic metal disks. The brown plastic case that measures 2.50 in. by 6 in., was received by my Father when he visited the Kawecki Berylco Industries in the 1970's. The company was bought by Cabot Corp. in the late 70's. The disks measure 1.25 in. dia. by .1in. thick. According to the description in the case the 5 metals are Beryllium, Lockalloy, Beryllium Copper, Columbium [an older name for niobium], Tantalum.
This is the tantalum sample. Click the Source link to see the samples all together, and here's a picture of the whole set:

Source: eBay seller jacav111
Contributor: Theodore Gray
Acquired: 27 December, 2008
Text Updated: 28 December, 2008
Price: $134/set
Size: 1.25"
Purity: 99%