Well, after all the fuss here, I was reminded that I had recently purchased a B+W Bay-III Yellow filter from B&H. It had to be special ordered and took a long time; it cost a bunch, too. The front is threaded still, but the filter element is, as previously described, glued in with what looks like silicone bathtub calking compound and there is no retaining ring. It must be an experiment in cutting production costs or something.