
The Caruba Step-down thread conversion ring (stepping ring, adapter ring, thread adapter, thread adapter) allows you to change the filter thread of your lens to a smaller one. This is especially necessary when you want to attach a filter or teleconverter to threads with a larger diameter.
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. In other words, if, for example, your camera lens has 82mm threads and you want to attach a 77mm filter to it, you will need an 82-77 Step Down adapter.