I'm not sure of the exact dimensions. It looks to me to be about 10" wide tops. It also seems to taper back to a smaller diameter down the tube. The tube is made out of fibreglass. It looks like it is very thin. It also breaks and cracks quite easily. All of the friction comes from turning the corner on the top side of the hoop. One key is to have a flat turning piece so that the rope doesn't always burn to the same spot. I've seen tennis rackets used and just some homemade hoops.

Mike Hill
H20 #907