This M & M wheel sewing head kit fits APQS machines that operate on horizontal wheels. These smooth-running wheels designed by APQS engineer Mike Moore glide across the aluminum rails for effortless quilting. The special hard polymer resists dirt accumulation and oxidation, and the sealed wheel bearings extend wheel wear. The kit includes one drilled and tapped wheel and three plain wheels, along with installation hardware and complete instructions. This kit fits APQS sewing heads on horizontal tracks, as well as sewing heads mounted on the Bliss Drive System. It is highly recommended to replace the carriage wheels with the M & M Wheel Carriage kit at the same time if your machine is not equipped with the Bliss Drive System.