I suspect your have 10 lugs on 7.25" bolt circle.
For that vintage they most commonly had a "clamp plate or ring" as Ed mentioned and then the lug nuts hold everything together, the wheels are piloted snugly on the hub.

Here is a picture of what that looks like.
Also in the picture is a newer lug nut with a large washer face often used without the clamp plate. My opinion is if the wheels/truck was supposed to use clamp plates then you ought to continue to use them.
https://picasaweb.google.com/lh/photo/SlJJGfds_gFZpL2YoQzTNdMTjNZETYmyPJy0liipFm0?feat=directlink

Also notice the nuts have little slots in them, a sort of lock nut. That particular style is called a "Marsden" nut and I've seen them as original equipment on many of these old trucks. Not sure when they stopped using them as lug nuts. http://www.lok-mor.com/products/marsden.htm


•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-