I was about to say that.
I was on a show a couple of weeks ago which used quite a few 7" as well as 6".
But I have to admit to a moments confusion over tube sizes!
(especially when you
a. haven't got an 8 to compare it with, and
b. people insist on using metric measurements - which I'm perfectly happy with in other aspects of life, but seem to have a real blind spot over in pyro!

)