Hi Salvatore,
I'll take a shot at giving it to you in inches. I convert from metric to inches almost daily, but rarely the other way around!
Everything on this bass is tapered, nothing is straight to reference dimensions from so I chose frets to reference from.
The 18th fret is close to where the large radius is tangent to the flat surface on the inside of the horn.
The 15th fret is close to where the other end of the flat surface is tangent to the radius on the end of the horn.
At the 18th fret, the cutaway is .850, the horn is 1.680. (The neck is 2.155, reference.)
At the 15th fret, the cutaway is .930, the horn is 1.475. (The neck is 2.080, reference.)
It might have been intended to be the only straight surface on the bass, hard to be certain.......... Hope this helps.
George