There are a number of reasons for "seconds" and it could be inappropriate to use the term "blems" as if it's cosmetic. First of all, in the manufacturing process, they are going to Q.C. every run checking on everything measurable, weight, length, etc. At any point in the process, production runs can be "shit canned", (the scientific term), and dumped in trays, mixing lot numbers and reasons for the rejections. It could be as innocent as mixing lot numbers, or a busted, or warn out die, necessitating a replacement, which might be "close" but not identical. It's impossible to list the reasons for rejection by quality control but it is not just because of finish or polish and you never know if you are getting a product that is measurably different from the standard, or it's just cosmetic. Whatever the reason, the maker does not want their name associated with their normally high quality product, so they sell this stuff cheap to people on a budget or someone who is not looking for match winning performance. In a lot of cases, it's good value and a good use of something that would normally be sold for scrap. Face it, there is a lot of scrap in machine shops. BB