I use the step-down ring on a Sigma 10-20mm f3.5 for Canon. The external thread does not fit in their entirety, therefore, the adapter can be screwed with some force on the lens. The screwing of various filters work very well, however, there are no problems! As I leave the ring permanently on the lens (not visible in the picture, only thicker filter then rise quite easily into the picture) does not bother me the bad processed further external thread. If you want the adapter but still spun on and off I advise against it, since you ruined the filter thread on the lens permanently safe!