Ducati Diavel Workshop Manual page 543

Tail light - number plate holder
Fit the left optical unit (13) and the right optical unit (1) on the compartment (23), inserting their pins (D) and (E) into
the vibration dampers (2).
Fit the split vibration dampers (H) into the corresponding holes of the compartment (23).
Fit the washers (14) on the screws (4).
Fix the optical units (13) and (1) to the compartment (23) starting the screws (14).
Note
The screws (14) must be inserted into the internal spacers (3) fitted previously.
Tighten the screws (4) to a torque of 6 Nm ± 10% (Sect. 3 - 3, Frame torque settings).