Funny how the bobbin plate covers go missing. makes you wonder what hapened to them? Girls saw and just pointed out that the "new" one was missing the same piece as the other two.
I saw a You Tube video about the mystery of the missing bobbin plates and the woman said it was because the bobbin plate is difficult to put back in if you don't know how it fits in, so a lot of them got left off. I'll to look up the video and post it here.
Here it is. It shows how to put it back in and explains why so many are missing:
http://www.youtube.com/watch?v=Fi8a_...eature=channel It is at approx 5:05 minutes into the video but the rest of it is worth watching for learning how to thread your 66, put the bobbin in and how to treadle....plus the woman is pretty entertaining.