Brother and Babylock changed bobbin size a couple of years ago for embroidery purposes. That foot could have been made for an older embroidery machine. The newer mechanicals will use the generics from Sewing with Nancy.
I've used these:
http://creativefeet.com/
I don't know about the newer machines, but I used them on older Brothers/Babylocks/Pfaffs/Vikings. Any low shank.