The plates may not take up as much thread length as you're thinking they do
http://rides.webshots.com/photo/2776297030080251109YhSQdn
They are countersunk, so the nut seats in them pretty well.
I believe the nut in the picture takes a 1" socket.

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-