I much prefer the 15 type bobbin system for FMQ, I don't seem to have much luck with the 301,201 or 66(I have them all). My favorite vintage machines for FMQ are Singers 237 and 15-90, I treadle both of them; the harp size on both machines is about 8 or 9 inches.
I can't find a darning foot that will fit the 301 and work properly.
Sharon W.