Where is filament thickness setting in Cura?
There are two important settings related to filament thickness in Cura 4.8.
They are in Preferences window (open menu Preferences &gt; Configure Cura):

Printers &gt; Machine Settings &gt; Extruder 1 &gt; Compatibile material diameter - this setting will influence visibility of materials available on the list in next point.
Materials &gt; Information &gt; Diameter - width of filament currently selected in the list.

Important remarks:

After selecting a filament from list you may alter its settings. But it will not become the active filament for printing until you press &quot;Activate&quot; button above the list.
Extruder settings (Nozzle size, Compatibile material diameter) will be always displayed with &quot;.&quot; (dot) for decimal point. But if your regional settings (in operation system) use &quot;,&quot; (comma) for decimal point, then the only way to enter new settings is use comma, otherwise they won't be saved. From my observations this defect concers only this single window.