If you think at the future you will want to use it one one of the European made sights with the metric thread, get it and the adapter. That said I have the one made for the Williams sight on an old Beeman sight on my FWB 124. I do have others on some Anschutz sights on other guns, with extension tubes so I can mount the sight body further forward to clear the safety on those rifles and still have the actual diopter close to my eye. Other than the thread the diopters are the same.