You can never have too many bobbins! It's a good idea to have extra bobbins on hand so you won't have to unwind one when changing your thread color. This clear plastic storage box comes with 12 Class 15 bobbins which fit most Singer class 15 sewing machine models. Be sure to consult your sewing manual to determine if this is the correct bobbin needed for your machine. Details:12 - Class 15 bobbinsReusable storage box