3.5cm tall, 3cm wide.
Made of plastic in Germany between 1945 and 1950 - I know this because inside, in tiny writing, is :
GERMANY US ZONE
I have been told that these were used to keep your holy medals safe, or as a container for little rosary beads
Or someone emailed me and said :
"if you have someone in need of a prayer you used to write their name on a piece of paper and pop it in the case"
I have the colours shown - please choose