Such machinery have adopted the connecting bar thread-taking-up mechanism, the rotating hook thread-hooking mechanism and the connecting bar feeding mechanism. Compared with ordinary lockstitch sewing machinery, such machinery have been equipped with the advanced computer-control system and their maximum speed can reach 5000 R.P.M. They can function in automatic needle stopping, automatic thread cutting, automatic thread-wiping, automatic needle positioning, automatic stitch-setting sewing and automatic bartacking.