Without actually measuring it I doubt anyone can say with 100% certainty what size socket you need.

Personally I would take from 15/16" through 1.25", and I would bet that it is actually a 1", or 1-1/16" as a second choice.

May be helpful to buy a medium sized 4 way lug wrench that covers 1" and 1-1/16".

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-