Velocity Stack for 40mm fan

Quick and dirty elliptical velocity stack for a 40mm fan. This has just about the largest possible internal diameter (38mm) without needing funky geometry to fit the screws in (which disrupts the "smooth" airflow)

Most of the other designs I saw were either too short for my taste or overly complicated without providing any real benefit, so I made my own version.

Does this actually help improve airflow?
Maybe. It definitely seems to reduce turbulence around the fan's intake side.