As a heavy duty lockstitch sewing machine, GB4-1 model is used to sew canvas, container bags, belts, leather, ... with alternating presser & reverse feed lockstitch machine. As a heavy duty lockstitch sewing machine, GB4-1 model is used to sew canvas, container ... shaft and reduces noise, ensuring the quality of the whole machine and prolonging service life. Oversize oscillating shuttle may be used ...