I finally did a minimal bit of research to see why ancient Chinese coins have a square in the middle. They're harder to counterfeit and they require less metal to create. But that's not all.
The hole was for storing coins - people could thread collections of coins on strings for ease of transport and saving. Now there have been millions of Chinese coins, given how far back their history goes. I put up a few pics of some of them that are still around for collection. The coin with a dragon on it is from Turkey; it's the world's oldest coin.
These predate China's use of round coins from 600 BC.
Ancient Chinese coin
“The dragon coin below is the oldest coin in the world.”