There are several different size bobbins(flat metal ones with only one or two holes, metal ones with holes all around, really flat plastic ones, and plastic ones that LOOK like they are the same size as the flat metal ones, but aren't quite) and they each fit different machines.
If you try to use the wrong one your machine may not stitch nicely...will probably sew, but there will be problems like skipped stitches, rats nest on the bottom of your stitching, incorrect tension, etc. Ask me how I know!!!!