HPS/MH bulb base size

OK, this is probably a stupid question, but since I don't know I am going to ask it.
Do 1000W bulbs use the same size bulb base as say 400W bulbs?
I have two 400W ballasts, one a lumitec electronic HPS/MH and the other the typical HPS transformer core ballast complete with hoods.
I am thinking of getting a 1000W ballast in the future as I have two functional light hoods. For some reason I have it in my head that 1000W bulbs are of a different socket size.
Will a 1000W bulb fit into an existing 400W hood connected to a 1000W ballast?

Thanks for your time.

bump bump....

I would imagine it would.

I had a 400W MH system and I upgraded the ballist and bulb to 600W HPS and am using the same reflector. The bulb was totally different in both shape and size but it fit into the same socket in the reflector.

yes.. it will fit.. all hid bulbs use what is called a mogul socket... they are all interchangeable so long as you update to the correct size ballasts, as fires and grows do not go together well...

Thanks everyone. I am not sure why I got it in my head that 1000W bulbs were a different size.
Thanks again!