the 420 will use class 15 bobbins, however, Brother SA154 bobbins are recommended as they are slightly shorter than class 15.... about 1/32 of an inch. You can wind any thread on them you like. From JAF or Hancocks I buy Gutterman 100% cotton thread in 50 weight... but I usually buy Connecting Threads Essential (a bit linty but inexpensive and strong) or Aurifil (pricey but very low lint), I also like Superior King Tut or Signature cotton for quilting.