When its cast, the round block you see at the bottom is solid, i had a machine shop thread it for a 2 1/2in pipe as you can see in the picture. And on the top they machined a 1/2 in down for my grate. I had to make it myself which isn't hard. I am closely connected because my grandfather owns the foundry that i work in and we make parts for them. I made my own pattern out of a, old nautral gas regulator that i found.