Car blocks

[Hotrod1]

I know this may seem elemental, but how do you build the 2x4 wheel blocks (in place of jack stands) to raise a car up to on and work under? dont want to try and re-invent them and want to rely on safety. How high can you make them? Nails, screws, how many, how long of material, etc. In fact, I dont even know what you call them.

Thanks in advance.