Tiniest Cuban Coin Ever!

As for world coins, of course there are smaller coin, hoever modern coins tend to be larger in size. Your coin has a diameter of 15mm (?) which is pretty common to see today. My smallest semi-modern coin is the 10 öre coin from Sweden, 1855-1872, with a tiny diameter of 13 mm. Here's an old comparison pic:

The later version of this coin was minted from 1874-1989 and had a diameter of 15mm.
Other modern coins today that have such a small diameter include the 5 Sentimo coin from the Philippines and the 1 Kopeyka coin from Russia.

I think the smallest 20th century issue is 10mm - the Panama "pill" is that size. It is the 2 1/2 centesimos denomination and is 900 fine silver struck in the US for Panama.

There are many smaller coins if you go back another 100 years. There is the 1 penney silver from England (Maundy money) at about 10 mm. There is the Fanam from India 5-8mm and the 1/2 Chuckram also from India at about 4mm.

Krause lists a 2x2 mm square 1/4 Jawa as KM#284 under Nepal in the 1701-1800 book. It weighs 2/1000ths of a gram.

Others that are smaller always invite arguments as to whether or not they circulated in day to day commerce.

I have seen an ancient coin smaller than the head of a pin in a display at last years FUN show. But that one needed to come with it's own microscope.

Usually what makes coins that tiny is because of their precious metal content relative to their denomination. The 10 öre coin I was speaking about earlier weights 2½ times less than the 25 Öre piece minted at the same time - a decently small coin, with a diameter of about 18mm. The silver fineness is the same, unlike later silver 10 öre issues. The Panamá Pill is a pretty thick coin, but weighs the same as a US Half Dime coin, 1.25 grams. I don't know what made the Panama government to issue them with such a small diameter, but hey, it's a piece of curiosity.

This impractical precious metal content and denomination scale becomes even more prominent in gold coins. There were frational US gold coin minted in California during the gold rush, tiny coins with gold value of $0.25 and $0.50 respectively since there weren't sufficient amounts of silver coins circulating and gold was so common. The original US $1 gold coin had a diameter of just 13mm but was increased to 15mm with tickness decreased because of contemporary complaints about losing such a tiny coin. But in ancient societies, population complaints weren't necessarily something to consider, so fractional gold was definitely a common sight.

With the wide introduction of base metal coins in the 20th century more practical sizes were used since the metal content was so longer important. But I forgot about the 1 Peseta coin, a tiny modern coin with close to no contemporary value (at the end worth about a third of a Euro cent).

I am under the impression that the Dutch 10 cents was one of the smallest coins before it joined the Euro. I could be quite wrong. I remember getting a few from circulation when I was there a while back.