Direct drive 4 Thread flat bed top and bottom differential feed overlock sewing machine with top and bottom feeding, high quality products with no twisting or plyshifting can be achieved. The top and bottom feed dogs are independently driven. The stopper regulates the path of the to feed dog just before it contacts the bottom ones, thus no wrinkle is produced on the fabric during sewing with increased feeding distance. large differential feed ratios can be obtained. these features increase feeding efficiency.