These are 5mm LED difffusers for small LED grids. They fit 5mm LEDs loosely, and are good for LEDs in a breadboard.
Grid sizes uploaded:
You can easily make your own custom sizes by importing the 1x1 diffuser into a design program and duplicating it. Then you can arrange them as you like.
I used this on a 3x3 LED grid on a breadboard to make a tic tac toe game with the Raspberry Pi. For more info, see https://electrothoughts.wordpress.com/2016/03/07/tic-tac-toe-arcade-game-with-raspberry-pi/.