I installed this on a project boat I have been building, along with a Millennium B-100 mesh seat - it's an awesome combo, perfect, works well and comfortable
Contrary to what was stated in a prior review, it DOES swivel, though there is a 'lock' of sorts which will make it not swivel, if you'd like to keep it fixed in place.
When new, there is a very tight fit between pedestal tube and the black pedestal top. Tight enough that if you don't have much arm strength and no experience with how these work, you may not be able to turn it, especially without a seat attached. Once it is bolted into place and the seat is on, however, it becomes easy to turn when you are sitting on it, or by hand. There is simply a lot of friction because the product is brand new. The tube and base *do not* swivel, only the top
The tube itself is 2 7/8" in diameter, and it is such a perfect fit that getting the seat base/top of pedestal off/on is difficult until it wears in a bit. As I later cut my pedestal down in order to sit lower, I sanded away some of the anodization for a 'quicker swivel', but that likely voids the warranty as the anodization serves to protect the tube from corrosion in the elements.