Any Help With This Coin?

So, I've had this coin about 18 or 19 years and never researched it much, just kept it safe. I've done a little bit of a search online as to what it is and it seems it's a thrupenny bit?
However, I'm intrigued to it's importance with it being mounted on the medal type object? I've read about gold ones of these too and this is certainly bright!

I apologise for the picture quality;





Many many thanks in advance, Dan.