Yes it is correct, diameter is measured one side to other straight across the center of the bore.

The confusion is I don't know of an 8 lug bolt pattern with 4.5" center bore.
I'd guess either you have something unusual or might need more care in measuring.

•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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