What do the H HO A and AO on the red button of the LR9D overload relay indicate?
TeSys D line overload relays and accessories
The H indicates that the device is set to hand reset mode, and the A indicates that the device is set to auto reset mode. When you add the "O" the red button can now act as a stop button as well. In HO the device is in hand reset and the red button acts as a stop button, and in AO the device is in auto reset and the red button acts as a stop button.