The "Chinese coins with the square hole in them" are known as "cash coins" in English. They were made over a very long time period, with the basic design of four characters arranged with one on each side of the square going back to the beginning of the Tang Dynasty in AD 621. Most cash coins are indeed CHinese, though the basic design concept was also coped and used in Japan, Korea and Vietnam. Specific designs were made for many years and often in vast quantities, meaning that some coins can be bought for just a couple of dollars, even though they are hundreds or even a thousand years old.
Genuine cash coins were cast in sand moulds. The ones bought and sold by the Feng Shui suppliers, however, are usually machine-struck modern replicas. Apparently, the replicas work just as well as genuine old coins for this purpose.
