Ducati SCRAMBLER 800 Workshop Manual page 403

Tighten the sensor securing screw fully home every time you add or remove a shim.
Measure the AIR-GAP.
Put the required shims.
Important
The sum of the feeler gauge must never exceed 3 mm.
Once the shimming is completed, tighten the sensor retaining screw to a torque of 7 Nm ± 10% and check
the AIR-GAP again.