One of the relatively unknown trivia about the design of the CD is how Philips decided on the size of the hole in the middle. The answer is so simple it is almost laughable. One of the engineers simply picked a Dutch 10 cent coin (dubbeltje) out of his pocket and used it as a mask. This means that if you put a dubbeltje in the center hole it fits but doesn't fall through. Amazing.

Unfortunately, with the Euro now being the official currency in the Netherlands this gets more and more difficult to demonstrate, because 10 cent coins are not in circulation anymore. So if you come across one, save it so that you can show this trick to your grandchildren when they admire your antique CD collection.

I haven't been able to verify this for sure anywhere (thanks stupot for getting me to research this), but my story is supported on where it says:

Did you know?
The size of the compact disc, the playing length and the size of the hole in the middle were determined during negotiations between Philips and Sony in the 1980s. They figured that the size of a (Heineken?) beer coaster would be "in the ballpark". The hole in the middle is exactly the size of a Dutch dime. The playing length was determined by the Japanese. The wife of Akio Morita, the president of Sony, played classical music, among which Beethoven's 9th (72 minutes). This had to fit on the CD. The inner diameter in combination with the playing length determined the eventual outer diameter of 12 cm.

There are also mentions on the following site: