Here we have the patent for Gian Robert’s most famous product - its distinctive chain pliers. The peg (7 in the diagram above) pushes the chain pin out. The dimple (8 in the diagram) is used to push it back in.
European mechanics swore by these pliers - by I found them virtually useless, or, at least, far too prone to damaging the chain. Give me the controlled precision of a screw type chain tool any day.