I took the 16" alloy Fiat rims to Larry Savage to have centre stub reamed out so they would fit the Sprinter. I had checked they needed to be a diameter of 84.1 mm and the fiat was 78.1mm. Larry pointed out that they probably did not need to be reamed or milled all the way through. I went home and measure the hubs and 10mm seemed to be plenty
The front was about 9.58 and the rear was at most 8.31mm. I asked Larry to make it 12mm to allow some clearance.
I checked the stub diameter and 84.0 to 84.1 seemed fine.
Here the measure is 83.87 mm.

The wheel bolts are 14mm tapered bolts 35 mm long with a 19mm hex head.
note only 20mm of the thread binds but nearly 30mm protrudes trough the rim as the first nearly 10mm of the hole is unthreaded. The tread continues and the bolt could be a bit longer with no problems.