High quality metal bobbins Hole for bobbin winding Singer Featherweight 221 and 301 compatible Three bobbins included The Singer Featherweight bobbins 3 pack are great to have with your sewing machine so you can easily put various threads on multiple bobbins and switch the bobbin out when necessary. These high quality metal bobbins fit various home sewing machines in all different brands of machines. The high quality also allows for the bobbins to flow more freely with less friction so you will not get skipped or irregular stitches while sewing. See the below information for compatible machines with these bobbins.