Ok, so I bought it... what the hell is it?

Stumbled across this item on UK eBay. Looks like it will be a nice peripheral addition to my collection of fractional farthings.
The details on the inset/counterstamp look too sharp to be homemade.
What is it?

The details on the inset/counterstamp look too sharp to be homemade.
What is it?
0
Comments
Experience the World through Numismatics...it's more than you can imagine.
<< <i>...The Penny hasn't been machined into and the 1/3 farthing stuck in by any chance?... >>
That would be my guess.
Roman emperor Marcus Aurelius, "Meditations"
Apparently I have been awarded one DPOTD.
<< <i>Yes, somebody routed out a hole in the penny and inserted the smaller coin. Makes me think of something somebody in shop class might do, just for the heck of it. >>
You might be right. OTOH, I think I see a circular flattened area on the portrait on the obverse, such as might be produced by counterstamping a coin. Since the host coin is a 1917, it would have to have been made that year or later.
So why would someone be counterstamping a penny with a die dated at least 15 years earlier (1902)?
Maybe it is a die trial of a counterfeit 1902 reverse die? Or an after-hours unofficial mint product?
"The Central Intelligence Agency owns everyone of any significance in the major media" - William Colby, former CIA director
<< <i>I think I see a circular flattened area on the portrait on the obverse, such as might be produced by counterstamping a coin. >>
It could also be a result of hammering the insert into place with a rubber mallet, on a hard surface.
I do like the overall effect of the reverse though.
1/2 Cents
U.S. Revenue Stamps