If you call the Parts Express hotline and ask someone nicely, they might be able to measure the thickness of the flange for you.
If you can wait until late tomorrow evening, ( 10 pm or so ) I may be able to take a measurement of the thickness of the exterior flange, IIRC it's around 1/8th inch, and the port flange is textured on the outside. ( flat portion ) I can also measure the outer diameter for you. Honestly, I would not recess it, as it's not very thick.
What this world needs is a good 10 watt loudspeaker.... one that can produce 10 acoustic watts without spontaneous combustion.