When the decimal system came to the Netherlands (about 1800) the 10-cent coin was named a "dubbeltje".
In Dutch slang, a dubbeltje was named a beisje, from Dutch-Yiddish beis, the value of two stuivers.
The central opening in a CD is exactly the size of a dubbeltje.
Ik legde een dubbeltje op tafel en dat werd de maat."
("The fastest decision in the development phase was about the diameter of the hole in the CD.