This machine adopts two straight needles, vertical-axis rotating hook with self-lubricating feature for catching thread loops and sliding cam take-up to produce two lines of double lockstitch . The needle bar can supported by ball bearings. It is provided with synchro tooth belt for driving, plunger pump for lubricating, knob-tupe stitch regulator and lever type reverse feeding mechanism . A bobbin thread pullback spring in the bobbin case guarantees the the harmony between needle thread and bobbin thread . Besides it features synchronized feeding of needle bar and feed dog .