Normally a coin with hole at the center makes it unique.
As compared to ancient times it is very rare to see a coin with hole within it.
The danish coins 1, 2 and 5 crone are the one which have hole in the centre of them.
Various European coins also had once.
Ancient chinese coins used to have have a squared shaped hole in the middle.
These coins were called cash coins.
The theory that you hear the most is that they put holes in them and then ran a string through the coins so that they wouldn’t be lost. If they had them all tied together there was less chance of losing them than having a pocket full of loose change.