The seat post was made from a left over leaf spring off a 65 mustang. But any leaf spring would do, if the leaf was think I would just cut narrower. I made it adjustable for different weights of riders and height by slotting the holes in the mounts. The down tube is a craftsman socket with a nut welded inside to hold the mounting bolt. All overkill to be sure I don't break anything and go flying. I used a cutting torch to heat and shape. Took an afternoon to build. The little spring was unnecessary, and I removed it, just arced the spring more. But it rides so so nice. I am 240 lbs and need a heavy duty ride. The old bikes used leaf springs and I’ve seen some here on the forum use them. One, the front forks has leaf spring, If I seen that earlier, Mine just might have a leaf suspension. I love this forum, so many ideas, and great people