It is pretty much clear now that part number 807166A3 is a manufacturing error across the board. They are a faulty design no matter where you buy them from. Whether it is Quicksilver, Sierra, after market, made in USA, made in China or Timbuktu or anybody else it does not matter. THEY ALL DON'T FIT. The last set I received (my third) looks very well made. On sight they appear to be of good quality and just what I needed, but they all are too big and won't fit into the Y pipe. Now, could my Y pipe be the faulty part and way out of specs? I don't know but I also don't believe it. There are too many complaints about this very same problem and then there are others who say they had no problems, fits just fine. Go figure! I will keep my last set and see if I can modify it so it will fit my exhaust pipe. If you buy these flappers be prepared to do some modifying. I hope Mercury and Sierra and anybody else that is manufacturing these flappers look into the matter and make some corrections and rewrite the production specs. Err on the loose side. No harm done. Attached are pictures with the measurement.