The C-153427 is the drawing number that the magazine is found on, and also became the part number. Drafting paper came in four regular sizes, A, B, C, and D, with A being the smallest and D the largest. They were filed according to the drawing size long before the days of computers, and knowing the drawing number was an aid in finding the correct drawing.
Shown is a WWII Springfield Armory replacement barrel for the 1911/1911A1. The drawing number is C 3838 - 4, with the 4 being the revision number. The D4 is the heat lot number.
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