These LED indicators should not be operated without a suitable series resistor or other current-limiting device. 8mm Mount, Round ; Square Lenses. LED illumination (contained within lens) Low depth behind panel (23mm max) Mounting Hole Size: 8mm Dia. Operating Temperature: -25 to +65°C Requires an external series resistor Maximum panel thickness 4mm PCB plug in sockets available, see stk. no ; 219-1041 219-1041 typically"