Adapter ring or thread change ring. With the Urth Stepup adapter, you can attach a 72mm filter to a 58mm thread.

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With the Urth Step-Up adapter ring, you can attach a 72mm filter to the lens' 58mm filter threads.
The first number in the product name is the male thread, i.e. the size of the lens thread, and the second number is the larger female thread, i.e. the size of the filter to be used, for example.
The Urth Step-Up adapter ring is made of 6061 aluminum.