It’s actually a piece of thin pvc pipe. They came with the USMC bikes. I believe it was to help cover the shiny forks for tactical reasons. The original ones were green so I obviously painted them tan.I find your use of a Upper fork tube guard between upper & lower triple clamps 'very interesting'.
I agree that it is Great that you understand the importance of protecting even the unused portion of the upper tubes.
Got ready to get it done yesterday but realized I was missing the torsion spring and rotor holder wrench. Ordered form Eagle Mike. Should be here in a few days and I'll get it done.That mid generation of doo-hickey was prone to breakage if not kept properly adjusted.