If you have the Herman Miller Aeron chair with the little levers for raising/lowering the arms and can't get them off, I run through how I did it in this video. TLDR:

I filmed this on my phone, so it gets cropped weird on desktop, view it on mobile!
the LEFT side is reverse threaded, so you have to turn the bolt clockwise to loosen it (ie NOT lefty loosey)
if it's turning endlessly, you just need to shove something hard/skinny (eg a small allen wrench) in by the lever to keep it from slipping 1:11