Luc, Eddie and Paco, thank you for the quick replies.
Wonder what Nikon is measuring
It's not easy to measure the depth of the FTZ adapter, the weather sealing between Z body and FTZ gets in the way...
With a digital caliper, I measured between 31.30 and 31.90 mm. [I did not push the caliper blades to avoid ruining the sealing]. If you average it out and subtract the approximate 1.20 mm of the weather sealing you get 31.60-1.20 = 30.40 mm, very nearly the nominal 30.50 mm that will bring the FTZ lensmount 46.50 mm away from the sensor (Z lens register is 16 mm).
the 0.10 mm difference is to be tolerated, I wasn't looking for absolute precision.
As for the height of the FTZ adapter, my measuring says 80.20 mm, a little more if you account for the white dot
The width of the FTZ adapter is 70.00 mm
Ciao from Massimo