Thank I had no idea what I was looking at.Step up/ Step down adaptor for filters.
You have a 82mm filter, but your lens is 77mm, you use a Step up (i think this is the right way round) filter so the LARGER filter fits on a smaller lens.
These are like a few quid for a pack for a cheap brand, instead of spending like £100 for another 77mm filter.
Those are nice B+W, but they make no difference to image quality.