I have seen sterling slings in the 37 pattern colour with the dog clips on one end. I wonder if they are related?
https://www.ima-usa.com/products/ori...nt=25651437317
And while I am trolling for other sten sling photos on the internet I found this photo ID'd as a stenmk2 mk1 sling. It is of fixed length. :
https://dbgmilitaria.co.uk/shop/inde...oducts_id=5921