The Levi's First Type Jacket 506XX has different specifications depending on when it was produced, but we can assume that it was produced between 1937 and 1942 because (1) the front buttons and box stitching are out of alignment, (2) it has a red tab, (3) the cinchback hardware is with a needle, and (4) the engraving of the letters on the front buttons is much deeper.
The color is considerably faded and the area around the elbow is clearly humanoids, which is quite hard It can be seen that it was worn by a man who was One pocket on the left chest. There is a slight discrepancy between the three rectangular stitches on the front panel and the position of the buttons. This is one of the ways to identify the model as being pre-1941.
patch
I think it originally had a leather patch on it, but it came off, leaving only the stitching on it.
red tab
A so-called single-sided tab with embroidery on the surface only. The red tabs on it indicate that it is not older than 1936.
top button
They have a reverse U-shaped stitching from the top button to the bottom edge of the front yoke. Many of the reprinted ones are stitched in a straight line from the front button to the side to the hem.
front button
The buttons are made of iron and the engraving on them is so deep and sharp that they are instantly recognizable as different from the buttons used in the post-war era.
front button (back), selvedge
The ears are used for the front placket. Also, the back of the front button is domed.
back cinch
Cinchback hardware with two needles, the part that receives the needle has a rough finish. Engraved metal fittings.
rivet
Front pockets, cinch back and rivets on sleeves." The "O" in "CO" is capitalized, so that it was produced relatively late, even between 1937 and 1941. It is presumed that this is not the case.