This guide concerns the older style(1970's-1980's) Campagnolo derailleur pulleys or jockey wheels as they are sometimes called. On many of these you will notice a straight "line" from the center of the gray plastic to the outer edge, usually at the peak of the tooth. Some sellers believe these lines to be molding lines or seams from production. They are in fact, cracks. You can determine this by placing the edge of a razor blade or exacto knife into the "line". I have one pair in which the "line" has opened up enough to see daylight through. I have also saved one pair by squirting super glue into the crack and squeezing it together. I would not use these pulleys at all. They are only good for display. I believe that the cracks are from age. I have seen them on SunTour and Sachs pulleys from the same era. I can find no documentation that these are production seams. If this is true, why do they appear randomly? They are CRACKS and one should not use these except for display. Jeff.