I like PPG DP90 black primer as a first and final coat for a working truck frame.

When I worked in a restoration shop that's what we used for parts that were supposed to be black but not glossy, and it holds up really good. We did several chassis with just DP90.
I had my frame powder coated to match the color and texture of DP90, and used it for my axles, springs, and other chassis components that were not powder coated.

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-