Special size for LONG-ARM MACHINES M BOBBIN CASES. EASY TO USE! Just drop A MEGA GENIE MAGIC BOBBIN WASHER into your bobbin case, replace the bobbin, and you’re good to go! Eliminates the backlash and bird’s nests on the underside of the quilt when changing directions at high speed. SAVES TIME! Less stopping and starting. Package of 12. Tough and long-lasting.