This is a MASSA 30mm-25mm Step Down Filter Adapter Ring. Step down ring allows smaller size filter to fit on lens with bigger filter thread size. It is a great way to enhance your photographic experience. You may also combine multiple step rings to fit even larger filters. Really a must have for all camera users.
Other Thoughts:What can I say, it works as advertised, a good adapter ring with solid structure. It allows the use of 25mm filters and accessories on a lens with a 30mm filter thread. I have useed it for nearly half a year. No problem found yet. Yet the price is reasonable. So I can say it was a good purchase, highly recommend this item to all of you.