In 1939 and 1940, as well as other years, 1/2 ton trucks were available with a pickup box (the common pickup truck), as a panel truck, as a suburban carryall, and as a canopy express. The fenders for the pickup trucks were wider than those for the panel, carryall and canopy express, because the pickup box was narrower than the other bodies.
The pickup truck was referred to as a cab type body, while the others were called single unit bodies.
Rear fenders for the single unit bodies were the same from 1939 through 1946. However, rear fenders for the 1939 pickup trucks were a one year only part.
I'm not certain, but I believe the only difference between the 39 pickup truck rear fenders and the 40-46 pickup truck rear fenders is that the 39 fenders are 1-1/2" wider than the 40-46 fenders. This is because the 39 pickup box is 3" narrower than the 40-46 pickup boxes, while both the 39 and the 40-46 models had the same rear track width.
Since the 39 pickup rear fenders are a one year only part, they are more scarce than the 40-46 rear fenders. Because of this fact, you may seem some rear fenders on a 39 that are actually 40-46 rear fenders that have been widened, using a 1-1/2" wide strip cut from a second set of 40-46 fenders. This evidently worked pretty well, as the shape of the two different fenders was identical, with the only difference being the width.
