It’s 35mm:
- https://www.rockler.com/dust-right-flexiport-power-tool-hose-kit-3-to-12-expandable [3]
- https://www.amazon.com/Cen-Tec-Systems-94434-Antistatic-Universal/dp/B07Q7SSTPX [4]
- from 35mm for 2.5" hoses: https://www.amazon.com/gp/product/B000WAAFXA
- hose: https://www.amazon.com/Bosch-16-4-Foot-Vacuum-VAC005/dp/B0000AV78B
- adapter machined out of plywood: Sweepy Dust Boot adapter