Hi Pattern Student,

I measured my pipe's OD and it comes out as 1.57 inches. Ron is right, ST pipes didn't have a pressure tap as manufactured, but since that picture I've added one to mine and polished the pipe as noted. I had another one twenty years ago and put a tap in that one, too, so I guess it may be common to find one with a tap. But the OD doesn't match the pipe with the screws as you have it marked, so it isn't a ST 60 sized pipe. They may have made a 90 sized pipe but I have never seen one.

Chuck