[Shop-talk] type of wrench?

[Steve Hammatt Mount Vernon WA USA]

I've got an instrument face to remove.  The lens is 
held in by a "ring nut" that has four external slots 
(90 degrees apart) that need a socket type wrench 
with four matching "tangs" that would engage into the 
slots.  I cannot use a hinged half-circle wrench that 
would be parallel to the face.  Anybody remember the 
name of the type of drive I'm looking for?
Thanks.

Steve Hammatt
Mount Vernon WA USA