It measures 3 1/2"x 1 1/2" and is meant as a 5 w marker. However, we fitted a 21w wedge bulb and powered it up for a couple of minutes and it didn't object, but gave a suprisingly piercing beam courtesy of that lense pattern! It fits beautifully below the rear light, just clearing the top of the bumper. Can't remember last time I was this happy!!
If anyone is interested, it is a Rubbolite 110/03/00 at just under £6 each (trade price). Oh and I picked up the complimentary christmas bottle of wine at the same time, (maybe thats why I'm so happy).
And wow are they bright! Didn't expect much, but they are better than those on any of the moderns I have driven recently.