This series of models adopts double straight needles and a vertical automatic refueling rotary shuttle to hook and slide the thread, forming a two row thread lock stitch. The swing of the needle bar and the synchronous feeding of the feeding teeth can ensure uniform stitching and prevent slippage of the sewing material. The knob type disc adjustment needle distance and lever type reverse feeding mechanism make the operation more convenient. The upper and lower shafts are supported by rolling ball bearings, driven by synchronous toothed belts, and equipped with a plunger type oil pump lubrication system. It is suitable for sewing shirts, uniforms, coats, women's underwear, jeans, etc.