To Adjust Needle Thread Tension - Singer s18 Service Manual

The upper thread tension should be 65 - 80 grams when pulling the thread (white polyester thread size 50)
at the speed of 110mm/sec with the tension dial at "4" (Make sure the foot is lowered.)
Tension dial (A)
TO ADJUST UPPER THREAD TENSION
Setting mark (C)
White polyester thread size 50
1. Set the thread tension dial (A) to "4".
2. Pull out the tension dial (A).
3. Lower the presser foot.
4. Adjust the tension by turning the dial (B).
To loosen the tension, turn it counter-clockwise.
To tighten the tension, turn it clockwise.
5. Push in the tension dial (A) aligning the "4" with the
setting mark (C).
Dial (B)
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