If you're talking about the tube a standard 2" receiver slips into, then yes its 2.5x2.5x .25 ga.
Most steel yards carry a specific 2.5 sq. Tube for receivers, its .25 wall but the seam on the inside is removed so 2x2 slips in perfectly.
It’s much easier buying an already made receiver tube and welding it on, don’t have to worry about the weld on the inside or trying to drill holes into 1/4 inch steel tube
I ended up buying a plain 2.5"x2.5"x.25" piece. It was no big deal filing the seam. It doesn't need to be filed smooth, just knocked down a bit. I have a comfy office chair and a TV in the garage and I watched the Preds beat Chicago while doing it.