The thread is me actually not accurate enough, the filter quickly eats pure. It is then a gefrickel, this again to solve the ring. Is probably because the thread is insufficient deburring, or at the finish. Under no circumstances should you turn bravely, but very very loosely purely screws. But then the ring is serving. It is flat designed, I do not see the filter at 16 mm at the full-frame camera, here is everything OK OK for the money, but not outstanding. Typical Walimex quality, but I would have expected more due to some reviews, I had also seen better Step-Up Rings for other diameters ...