120mm Inline Fan connector with cartridge holder

I had an inline bathroom fan, and I needed to add a carbon filter (for an SLA printer) and some ducting to it. Active Carbon filter mats are cheap, so I made my own cartridge holder and cartridges.

Holder and lid of choice (either for 100mm round flexible conduit or 55x110 square conduit screws to the base with some 4x20 wood screws. I put some regular painters tape on the edge of the box as a gasket, which is enough for this purpose.

My inline fan had an outer diameter of 120mm, so I made