I replaced the lower half of the seat tube on my Yo last year using True Temper OX Platinum. It's a standard diameter.
I meant to ask about this a couple of days ago, you replaced the lower half of the seat tube? Why not replace the whole tube and/or what was done with the seam?
The tube was rusted out at the bottom, so that had to go. I figured I would replace the press in BB with a threaded one while I was at it. I cut the seat tube above all of the corrosion and replaced the lower bit because replacing the whole tube is tough. Getting a clean cut where the stays and top tube are is a chore.
I butt welded the new tube into the old one then just hit it with a file and some sand paper. There were one or two low spots that I filled in with silver then sanded down again. if you didn't know the work was done you wouldn't notice it. Only by running your hand over the area can you really tell.