I don't remember the exact measurement, but Paragon 44mm head tubes are the smallest ID of any that I've used. I think I have one in my shop that I can measure later today. Some of the straight walled tube that is made for 44mm head tube stock is very close to 43.95 on the ID, so I don't like to use that stuff.

Any pucks that I make get a 1 degree taper that is only the target OD at the very bottom(Paragon's have a good size chamfer on the ends, so you can go slightly oversized) This makes it so that your part doesn't get stuck on the puck from distortion and makes it easier to get the frame back into the jig after welding/brazing.