First look in your shop/service manual.
It will describe and show different front axles and will also give specifications (usually at end of the section) for king pin diameter and so on.

For the 48-54 trucks, and likely a few years either side, the 1.5 ton axle is based on the 3/4 and 1 ton axle beam with same king pin but different hubs and brakes.
The 1.5 ton axle has a screw on dust cap over outer wheel bearings.
The 2 ton (and 1.5 ton heavy duty) axles have a thick flying saucer like dust cap held on with 5 little hex head screws. These axles also have 1.109" kingpins.

This only for 1.5 and 2 ton Chevy and for most GMCs of same size. Not speaking to GMC's larger trucks which could have even more different different axle options.

•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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