Power cable identification

[Josh Dersch]

So I know for certain that this topic has come up before, but I cannot 
for the life of me find the thread(s) it appeared in, so I'm asking 
again (apologies in advance).

What is the name of the rounded, 3-pin power connector often seen on 
early test equipment (I've seen it on older HP and Fluke stuff)?  I have 
an S-100 chassis that inexplicably uses one, despite dating from 1982 or 
so.  I need to track one of these cables down but I have no idea what it 
is exactly I'm looking for...

Thanks as always,
Josh