The parts book shows wheel #602606 for 1937-38 and 39 cars and 1/2 ton trucks. Described as wire wheel, 18 X 3.62 rim width for 5.50 X18 tires.
A hub cap is not listed and it not the same wheel used for the 1936 or prior 18" option.
When I go to the 1939 truck data book. 1/2 truck shows a 5.50 X 18 tires option. Describes the wheel as short spoke steel disc. Rim width 3.62". The 5.50 X18 option is described as (high wheel) gives more road clearance for use on muddy roads.
Guess that is as clear as mud.
