Sequence of Lock Stitch Formation

Red thread = Needle Thread

Green Thread = Bobbin Thread

Fig 1: the needle is at the top most position

Fig 2: the needle penetrates the fabric

Fig 3: the needle thread is caught by the hook of bobbin

Fig 4: the needle thread is carried around the bobbin

Fig 5: the needle thread is knocked over bobbin thread (interlacement)

Fig 6: the needle moves to the top most position and the lock stitch is formed