Diameter depends on truck model, measure what it came with. Commonly 1/4" and 3/16", sometimes 5/16".

Not much trouble to bend, much can be done with bare hands, tighter bends will be easier with an appropriately sized tube bender.

•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-