The RS-11 electronic bobbin winder is perfect for using with standard lockstitch 21mm bobbins or larger ones up to 28mm in diameter. It's easy to install and operate, with an On/Off switch and a thread tension adjuster. This amazing tool even comes with a thread cutter blade and automatically shuts off when the bobbin is full. It fits all types of bobbins, including Type M, Type L, Type 15 (Universal), or any with a 1/4 inch (6.4mm) center hole.