"I wanted to create a quick fastening system and universal adapter plate that would allow HVAC contractors to perform duct ...

Pinwheels are pretty optimized from a design standpoint, and are so cheap and easy to build that putting a pinwheel to work as an HVAC duct flow meter seems like a great idea. Great in theory ...

That didn't meet our local codes, so we contacted a heating equipment supply house ... We also bought a few rolls of UL181 ...