Number plate light size

I think there are a few different fitments, some cars seem to have one size and others have another size. Only real way is to take one out, they're not difficult to take out.

For what its worth, my June 2007 car had W5W bulbs
 
Mine are 501 W5W as with the sidelights and interior lights.
 
Mine were festoon bulbs, not 501's like side lights.
Every car seems to be different regardless of age.
It's same with boot light.
Only way to find out joe is pop a light out.
 
wasn't it your car jase that had the lights behind the sun visors though or am I thinking of someone else? maybe that was woodys..