Great work! As usual, I'm blown away by the stuff you make. You are in a class of your own.
You say you made the nylon fittings? How does one even start to do that? I've used off-the-shelf nylon plumbing fittings but never considered making my own from scratch. And I've never even heard of a titanium spring pin before.
I might have to challenge you on this being the lightest buck saw ever, however. In the early 1970s Larry Penberthy (father of MSR) sold a similar saw blade that could be connected to the top, inverted U shaped aluminum tubing piece, of the MSR frame packs sold at the time. When assembled it created a buck saw with a depth of cut from 6" to 12" depending on the size of the pack's top piece. On one backpack trip he demonstrated the saw by cutting through a 6+" diameter tree that had fallen across the trail. I carried the blade for all the years that I used the MSR pack but never used it to cut anything.
The reason I challenge your "lightest" claim is that the frame of his saw was multiple use with the primary use being the top part of his frame pack. So the net weight of the saw was the blade plus a couple of screws.
I would call your saw the lightest, self contained, non multiple use saw in this universe, however.
Keep up the good work.