It is used to raise and lower the presser on the knee. Normally, You will be able to raise and lower the presser foot using your knees without using your hands. Push the knee lift lever to the right to raise the presser foot, and return it to lower the presser foot. There is no need to raise or lower the presser foot by hand, improving efficiency. it is attached to the sewing machine accessories, so you do not need to purchase it separately. If the Knee Lifter is damaged or lost, you can only purchase the Knee Lifter.