Goodbye PC4-M6 Coupling!!
No extra bolts needed.
There are little teeth lining the inside of the clamp for extra hold. That tube ain’t going anywhere!
Shove the tube into the hole (use needle file, careful not to file away teeth), trim/shape as required.
Install optional 3mm led, bend legs.
The LED legs will just protrude out the top, so you can either use a coin battery 2035 or dupont connection.
You could use a dupont connector as a cover if not using the LED and you don’t like the legs protruding.
Maybe add a resistor to reduce the brightness.
Pics need to be updated with newer version which has a lip to eliminate the light gap.