The lockstitch formation uses two threads - a needle thread and a bobbin thread. The needle moves down to form a loop in the needle thread, which is enlarged. The bobbin hook then catches this loop and passes it over the bobbin, interlacing the two threads. As the needle and thread take-up lever rise, the loop is drawn up to form a complete stitch and prepare for the next stitch.

1. PRINCIPLE OF LOCKSTITCH
FORMATION
• Lock stitch is formed with two
groups of threads i.e. needle
thread and bobbin thread.
• The needle moves downward
and reaches the extreme
lowest position. Again it rises
up a bit and stops for a while.
As a result, a loop is formed in
the needle thread.

2. • At the same time, thread
take up lever also moves
downward. So it aids the
formation of needle
loop.
• Then needle loop is
enlarged.

3. • The bobbin holder hook
catches the previously
produced needle loop and
passes it over the bobbin
case.
• Interlacing takes place
between bobbin thread
and needle thread loop.

4. • The needle along with
needle thread moves and
the thread take up lever
also moves up.
• Here loop clears bobbin
and take up starts to draw
thread up.

5. • Here take up draws thread
up and loop is closed.

6. • Here feed material
moves for next stitch
position.

7. • Then needle descends to
lowest point for
subsequent stitching.

8. • Finally new loop has
been formed and is
passing around bobbin.

9. • At last loop is pulled up
to make a complete
stitch.