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123 Block Links: Blackened!
While looking for something else, I came across my bottle of Aluminum Black, so I just had to do this:

123 Block Links – blackened Looks much snappier than the originals:

123 Block Links – trial assembly Those are plain old alloy steel cap screws with a black oxide finish.
The Aluminum Black package directions tell you to apply it with a swab, rinse, and repeat, which seemed like a lot of work for a handful of pins. Instead, I poured a little into a pill bottle, dumped the pins in, and gave it a good shake to coat the pins, whereupon the cap blew off as the contents proceeded to boil merrily. A quick cold-water rinse calmed things down, with no particular harm done, although I had to chase the threads with a tap to get the black powder out. A layer of oil prettied them up nicely.
Today I Learned: the reaction between selenium dioxide and bare aluminum is strongly exothermic.