NASA shot down lock washers in 1967, but still required them until 1986.
Government is particularly schizophrenic.
We were issued optics for many years that were metric, but all the literature and longer ranges were in yards... schizophrenic.
While most all military small arms are gauged in metric, velocity ratings are still mostly displayed as feet per second... schizophrenic.
NASA just lost a Mars probe a few years back because part of the programming was in metric & part in feet/inches...
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As for brass button manufacturers,
The manufacturers of buttons also made everything under the sun, from bellows for atmospheric pressure gauges (a SUPER long closed case) to extruded tubing, and everything in between, from clock parts to adding machine parts to trinkets.
Buttons paid the bills for the expensive processing machines.
Singer (sewing machines) made aerospace components, up to including the moon missions & nuclear bomb triggers...
Pinball machine companies made land mines & bomb fuses & triggers.
Ely Whitney made cotton 'Gins', separated seeds and seed pods/stems from cotton fibers.
Ely Whitney also made cannon carriages & gimbals, artillery sights, firearms locks, Sam Colt's early revolvers, pad locks & door locks, governors for steam engines, etc.
My little machine shop is mostly supposed to be welding & small batch widget making, while the bread & butter contracts are for the DOD/Navy, a far cry from welding up broken farm equipment and bending tubing, what I intended to do.
I don't like to be micro-managed or have hard deadlines, it interferes with my watching cartoons, jeep crap, reloading crap, going shooting or fishing...
My best seller when I started out and had virtually no equipment, believe this or not, was reproduction padlocks, circa 1870 or so.
Winchester, Wells Fargo, B&O RR, US Marshall, ect. stamped into the brass sides, riveted together.