Italian system:
This system has levers, which are firmly welded-on the M-section!   There is a bowl with a loose clamping ring on the V-section!
This ring has to have a sharp edge where the levers of the M-section engage.   In order to determine the size of the Italian coupling, you either have to measure the external diameter of the V-section or the internal diameter of the M-section.   The external diameter of the V-section or the internal diameter of the M-section has to be equal on the M-section and V-section.   The coupling hose bushing is measured outside or on the internal hose diameter.