1954 Job Rated Truck Question

From : md42martin

Q: hello group. i have recently purchased a 1954 job rated h truck witha dump bed. totally original from kansas...no rust original paint....always garaged. a real beauty. anyway...i want to understand what the job-rated h designation means. i have also heard of job rated g and job rated j trucks. what does all this mean thanks in advance. mark debellis westchester ny mark debellis md42martin@aol.com .