I know.
I have no idea what mm is referring to in terms of the current century — perhaps a relic on the High Line.
Don’t get so high and mighty - I was riding the trains when you were in short pants. Perhaps I’m thinking of the bar above the seats almost out of my reach; but then when you have to endure inner-city brats hang-gliding over your head (and ignored by police) on the Grand Central shuttle - you don’t notice the disappearance of straps.