A holder for 5mm LEDs on my model railway system. In this particular case, I connect the LED via a 1kOhm resistor to the unused outputs of the MCP23017 extender on my DCC-EX controlled model railway. I let the LEDs flash underneath the system as an indicator as to whether the I²C bus on the respective device is still working. The LEDs are used for quick debugging.
When building, first shorten the connecting wires on the LEDs and solder on the resistor and cables. Then pull shrink tubing over it and bend the connecting wires. Then insert the LED into the holder from the inside. If necessary, press in the LED with needle-nose pliers. It then stops on its own.