Here is an o.g. seat post that my friend Bill sent me to copy.
I had to file a bur off of the large diameter to get the large nut piece to slip off. This is also the seam where the .5 threaded part presses into the upper piece. I can not tell if Sears sweat brazed the two pieces together because of nickle plating,
I decided to make the seat post for my cannonball bike one piece, which meant a lot of turning lol.
Here is the piece almost done, I still have to cut a groove in it and drill a hole for the top bolt, but you get the idea. The other ones that I plan on making will be two pieces just like the originals.