Just how big is that driver?

Unsound
Well, yes, and no.

I'm serious as to the figures a maker uses for the products they sell which have other makers drivers in them.... Why should a given driver's specified dimensions then differ from those of the provider of the driver being used in the first place?

For example, If I go about building speaker systems... and am able to buy for instance, drivers from Vortex for ex., and Vortex says the drivers I want to use are 9inch, 5inch, and 1 inch drivers, should I be then compelled to say the Drivers in my speaker system are 10 inch, 6 inch and 1 inch?

Or merely pass along the orig drivers specs? this latter approach seems prudent and wise.

I just happen to have a NHT 1259 "12" Woofer on hand.

Overall dimension..310mm which is 12.24 inches
Mounting hole......281mm which is 11.06 inches
Cone diameter.........................9 inches

Nobody ever made a rule I guess that the size stated of a driver is of the cone alone(or cone and attached surround), most seem to think as a logical assumption the measurement provided is of the actual cone surface area, but it is instead of the Driver's entire assembly, which seems to coincide pretty consistentley with first hand experience shown here by the examples above.

That is why women can't park their cars because we tell them 6 inches is really 12!

The sub I have is sold as 12", which is the size of the mounting hole, so the size of the driver is a bit smaller.

I'm 5'10" but think I'm taller!