Brother ST4031HD Operation Manual page 18

3. Pass the thread through the eye of the lower
looper.
4. Slowly turn the hand wheel, and make sure the
returns to the original position.
NOTE:
If the lower looper thread breaks during sewing,
cut and remove thread from both of the needles.
Before re-threading the lower looper, make sure
that the lower looper re-threading is done exactly
as diagrammed. The machine will not operate
properly if the threading is not done in the proper
sequence.
CAUTION
Thread the needles after the lower looper and
upper looper have been threaded.
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