Sennheiser 424

Those are indeed excellent looking

That's the one! I would never guessed it was a Sennheiser. Astonishing how thin and surprisingly simple it looks.

hd424x specifically. The normal hd424 has black sides, the 'x' has silver ones

Sennheiser 424

black plastic labels is the later 600 ohm version, both the original 2000 ohm HD424 and HD424X have silver metal caps, the only visible difference between 2000 ohm HD424 and HD424X is the name on the packaging

I believe also tge colour of the driver housing, which was white on (some) hd424x

2000 ohm beast