This black metal pipe is available from Home Depot. It is really about 1 and 7/8ths inch in outside diameter. It is marketed as 1.5 inch inside diameter pipe.
The stock lengths of this pipe are ten feet long with threads at both ends. Home Depot will cut this to whatever length you need and thread it for you if you like.
I picked this 55 inch length off the shelf with threads on one end. It was left over from a previous customer’s cut.
I wanted the threads so I can spin on a cap at the top after the antenna is installed.