This slim duct was designed to house a 40x10 fan, and comes with a mounting ring that allows for easy tool-less removal and adjustment of the fan's direction. I designed this for my terrarium to shield my fans from mist and excess water, so there is a deep grille which sets the fan back from the opening and directs airflow forward. The mounting ring lets you to easily adjust the direction of the fan, and allows removal of the duct for fan maintenance. I printed mine in PLA+, but other filaments would work equally well.