Stupid question but ...
why do you ask ?!
I don't know the answer to the question, but wondered myself what these things were built with when I considered seeing if I could "make my own surge protected 13A outlets" for my cinema room...
anyway if this is why you're asking, Clipsal actually do some double gang 13A surge protected and surge-protected plus clean earth outlets.
Don't know if this helps or is relevant though.