... heavy duty lockstitch sewing machine, GB4-1 model is used to sew canvas, container bags, belts, leather, tent, luggage, etc ... heavy duty lockstitch sewing machine, GB4-1 model is used to sew canvas, container bags, belts, leather, tent, luggage & thick ... oscillating shuttle may be used to increase thread volume and to reduce number of times of thread change-over to enhance working efficiency.Max ...