Duerkopp Adler 550-16-26 Operating Instructions Manual page 7

4.4 Setting the Thread Regulator
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Caution Risk of Injury !
Turn the main switch off .
Set the thread regulator only with the sewing machine turned off.
The needle thread quantity required for stitch formation is regulated by
the thread regulator 6.
Only a precisely set thread regulator assures an optimal sewing result.
With a correct setting the needle thread loop must glide over the
thickest part of the hook with a light tension.
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Loosen screw 5.
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Set the position of the thread regulator.
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Tighten screw 5.
Setting note:
When the largest thread quantity is required, the check spring 7 must
be pulled up approx. 0.5 mm from its upper end position. This is the
case when the needle thread loop passes the maximum hook
circumference.
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