Encoder wheels are an important part of APQS Perfect Stitch regulation. Two encoder wheels are used on each stitch-regulated machine---one for the front-to-back direction of the sewing head, and one for the left-to-right movement of the carriage. The encoder wheel helps translate your motion into signals the machine's circuitry understands. As the wheel rotates with your direction changes and movement, the machine places stitches precisely where you want them, at the stitch length you have chosen. Encoder wheel life can be extended thanks to built-in adjustability to the wheel's placement. When the maximum adjustment is reached, it's time to order extra encoder wheels. These encoder wheels fit the following APQS models: Millennium, Freedom SR, Lenni, Lucey, Larry, and Liberty. This part fits all generation models.