That is an interesting theory about race car mounts possibly referring to the method instead of the mount itself. You might be right!

Regarding the other elements, the post says he is mounting his home made seat and says those vertical sections of pipe are seat posts that he welded on himself. As for the square tubing pieces with the little bolt loops, I assumed (possibly incorrectly) that these were some sort of pre-made thing. If 1.5 tube is common, then clamps for it must be too? Or maybe I'm assuming too much that the square tube universe would be like PVC pipe is, an elbow, joint, or adapter for everything.

I thought about sourcing some slightly larger tube to manufacture my own.

The biggest issue for me is, I don't currently have a Bacchetta seat. If i did, I'd have a seat in one hand and the frame in another, and I'd figure it out. But I don't want to make a ~$300 mistake by buying a part that obviously (to those in the know) won't work. I've already made that mistake with things like top tubes, threaded vs nonthreaded fork stems, bottom bracket sizes, etc.

Quote Originally Posted by darnthedog View Post
If you look at the picture closely. You will see the clamps are nothing more than larger square tubing that fits around the frame tubing. They have a small round tube welded to each side. Guessing a 1/4-20 bolt, Maybe a bit smaller.
There is a tube welded to top of clamp. That is where it looks to have a couple handle bar clamps mounted to hold the mesh seat frame.
As to race car mounts- I am going to make an assumption here that he is referring to how they are mounted, not that they are from a Race car.
The Mesh seat on that photo is home built as well.