Board stacking is simply the process of taking 2 or more prototyping boards and fixing them into a vertical stack. The main reason for doing this is to build systems that are bigger than just 1 board.
All the Protostack Large, Medium and Small boards have a common form factor. This is what makes stacking possible. The full size boards have 6 mounting holes whilst the half size boards have 4. The diagrams below shows these holes and dimensions.
When you create a stack, you use a combination of m3 screws, m3 Male/female spacers and m3 female/female spacers to fix the boards into place. The diagram below shows the arrangement of these components.
In most cases, you will want to share power and data between the boards in the stack. There are many ways of doing this. One way is to use stacking headers. These are similar to standard 0.1″ (2.54mm) female headers but with longer pins. These stacking headers were carefully selected to fit 10-12mm spacers and are ideal for running data and power between boards in a stack.