Hey Richard,
As scholar noted the threads are 3/4 BSP. I found some QD end fittings from Menards that were 3/4 BSP and had a 3/8” barb. They initially were a tight fit with the Festool tubing, but after some heat gun action on the Festool tubing, they acquiesced. They fit so tight I probably didn’t even need to use clamps.
Tubing for a vacuum situation can be problematic. If the wall thickness is too thin or the durometer is too soft, the tubing can and will collapse.
That’s the reason I decided to just purchase the Festool tubing rather than to reinvent the wheel. If I needed 200 feet of vacuum hose I’d probably considered 2nd sourcing, but for 15 feet, Das macht nichts. [big grin]