A: It's supposed to fit over a 1.66" OD galvanized post. I ordered 4 of these plates, and the holes in all of them were too small for that pipe
A: 1 1/4" Schedule 40 / 1.66 Outside Diameter
A: The pipe collar can accommodate a 1.66" Diameter pipe.
A: It is big enough to handle the pipe sold from the same company. Don't purchase the larger footing if it needs to sit in deep muck/mud.