Like others, I bought a couple of HM40's 2 years ago. I have mixed & matched with Peltor & David Clark headsets with no problems.. .. .They can push your sunglasses into your head after a while, though I doubt if they are unique in that!. .. .Anyway, we'll need sunshine for that to be an issue. <img border="0" title="" alt="[Cool]" src="cool.gif" /> . .. .BtB