If you're buying Wet Sounds speakers, I know you can call them for the info. I installed a set for a customer last year but cant remember the size they were.
It's a 2" bar if I remember right, but depends on which way you measure, as it's horribly elongated. I used 2-1/4" clamps and milled down the mating surfaces of the clamp halves so they would bite.
I am selling those skylon speakers i bought from you, i keep running into problems (money) to buy the amp.. i put them on ebay so if you know anyone wants to buy them there up there.