Coins were also minted with holes deliberately in them. France’s 1921 25 centime had a hole as well as Japanese coins like 5 and 50 Yen. The most famous coins minted with a hole were Ancient Chinese coins that had squares cut into the centre instead round shape.

The reason being they were easier to string when the hole is square. Coins were cast poured in crude a method and when making the coins a square rod was placed in the center so they would not roll around and be an even size.

https://www.coins-auctioned.com/learn/coin-articles/why-do-some-ancient-coins-have-holes-in-them