Velocity Stack and Fan Guard for 40mm Fan (round)

This is a velocity stack for a 40mm fan (recommend 40x20mm).

Designed for fans with a 21mm diameter hub/motor.

With the right duct and fan combo a velocity stack will help boost the airflow through a duct system, and will also protect the fan from foreign objects. I aim to make all my designs elegant, efficient and effective. The 3Es! Feedback is always welcome.

The design features of this compared to others is:

1. Has small holes around bottom to control and boost air flow (boundary layer control).
2. Has the right size holes and design so that 3mm socket head bolts can be used.
3. Designed to printed without support or brims.

A version with a flat side is also available:
http://www.thingiverse.com/thing:2211722

Please check out my other thingis!