18" dual wheels will be hub piloted, so will replacement 19.5" wheels, so no countersunk lug holes in the wheel for the lug nut, just straight holes..

It's my opinion that you can use 1/2" studs with 9/16" holes in the wheels, but if you want to change studs sometime that'd be a great idea.

I switched from 7.50-17" bias tires to 8R19.5 and it made a lot of difference in ride, smoother and drove better.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-