Singer 6660 Instruction Manual page 27

STRAIGHT STITCHING
The correct appearance of your stitching is largely determined by the balanced tension of
both top and bobbin threads. The tension is well balanced when these two threads 'lock' in
stitching is irregular, you will need to adjust the tension control. Make any adjustments with
presser foot 'down'. A balanced tension (identical stitches both top and bottom) is usually
only desirable for straight stitch sewing.
ZIG ZAG and DECORATIVE SEWING
For zigzag sewing and decorative stitch functions, thread tension should be less than for
straight stitch sewing.
You will always obtain a nicer stitch and less puckering when the upper thread appears on
the bottom side of your fabric.
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