Might be a silly question but does any one knows what screw size should I be using if I want to mount the Particle Boron on a surface using the 4 holes on the corners of the board, or sandwich the board with another board like the Adafruit Featherwing series boards. See screenshot below. And where I get these screws. I am not able to find these screws in my local hardware store as they are rather small. Are these specialized screws? Thanks.