Adapter ring is to be used when a filter or accessories have different size with the thread size of your lens.
For example, if your lens has 52mm threads but you have an 58mm filter then you will need a "52mm - 58mm" adapter ring.
The first figure is the thread size on your lens whilst the second figure is the filter size.
Many people mix up with "focal length" and "filter thread size" of a lens because both take the same unit, mm.
Please ensure the right size you need before bidding or send us a photo of the front of your lens and let us know.