This CD 257 has fizzures in the threads similar to the kind you see in WFG 121's. And there's thin, elongated bubbles lining the fizzures. The elongated, thin bubbles go all the way down into the wire ridge. There are other thin stringy looking bubbles in the shape of circles to. Weird defect ive never seen in a CD 257. Amazing glass clarity makes it even more noticeable