I have the same bracelet as yours and, coincidentally, also have only one endlink. The single endlink on mine is also different to the one that you have and is unmarked. I also have the same bracelet as these Ebay examples and can confirm that the endlinks are interchangeable with your bracelet (you might need to refinish them).
https://www.ebay.co.uk/itm/394652138416Purchases made through these links may earn this site a commission from the eBay Partner Network
https://www.ebay.co.uk/itm/145616596010Purchases made through these links may earn this site a commission from the eBay Partner Network
What I can't confirm is whether the endlinks on either will fit your Polerouter.
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