Ducati Monster 620 Owner's Manual page 102

To change the preload of the spring inside each fork leg,
turn the adjusting nut (2) with a 22-mm hexagon wrench.
Preload setting range (A) is from 25 to 10 mm
Factory setting is 18 mm.
Important
Adjust both fork legs to same settings.
E
30
3 3
fig. 18