Here is more info on this attachment
http://www.ebay.ph/itm/RARE-Greist-O...-/390326410594 . Mine is black like the one I linked to above, but if you look at the two pictures you will notice the difference in the part that attaches to the needle bar.
I have tried it out, and not 100% sure exactly how to use it, but it did overcast!
So, anyone else have one of these??? Or know how to use it???