Bobbin Toppers are the fun and practical way to store your bobbins. If you're tired of misplacing your bobbins and having to hunt them down, hunt no more! With Bobbin Toppers you can store each bobbin with its corresponding thread spool. The Bobbin Topper is uniquely crafted to fit most home embroidery and sewing thread spools. To prevent unwinding of bobbin thread, simply use the thread lock slit on the side of the bobbin topper. Fits Spools with larger holes 3/8in - 5/8in diameter. (Like Aurifil).