only these are not on a plaque they are all seperate, there might not be a specific name for them I was just curious, obviously from some of the replies this forum allows children to join up, any grown up building forums you know of?
Seems they are just called house numbers , or at best singles or flats.
Have a look here, they call them house numbers and it looks like that's all they make http://www.sign-maker.net/brass-letters-numbers.html