Several soft iron pins can cling, one below the other, from the pole of a magnet because the bar magnet by induction magnetizes an iron nail which gets attracted to the magnet and clings to it. This magnetized nail magnetizes the other nail near it by magnetic induction and attracts it.
This process continues till force of attraction of magnet on first nail is sufficient to balance the total weight of all the nails in the chain below it.
