Brother 681B-UG - Manual (Page 17)

THREAD TENSIONS
It is important that tension of upper and lower threads be equal to prevent puckering of
material or other problems.
It is recommended that a test sample be made before starting to sew.
UPPER THREAD TENSION
To regulate upper thread tension, merely
turn thread tension dial with your thumb
after lowering the presser foot.
THE HIGHER THE NUMBER, THE
TIGHTER THE TENSION.
To increase tension: Turn dial to right to
larger
number.
To decrease tension: Turn dial to left to
smaller
number.
NOTE: The zigzag stitch requires less upper
tension than the straight stitch.
LOWER THREAD TENSION
Although lower thread tension has already
been adjusted at the factory, when sewing
very thin or heavy materials it may have to
be readjusted.
To regulate the lower thread tension, turn
small screw on the tension, spring of the
bobbin case with the small screw driver.
To increase tension: Turn the small screw
clockwise very
slightly.
To decrease tension: Turn the screw
counterclockwise
very slightly.
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