It consists of a plastic sleeve with a spring inside, 
which clicks the pin in and out.
Installing the shelf is really fast thanks to the intentional leeway of the smooth pin heads, which slot into position without damaging the holes, even off-line holes.
Adjusting the position of the shelf is easy and intuitive: just by pulling back the shelf-locking clips the pins click out of the holes.
SPRING is available with 5mm or 4mm pin.