Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2337382.

Small ventilation grill with rounded 50mm ends and hexagonal grid. The size of the panel cutout needed is 100x50mm (approximately 4x2"), and the vent has an overall size of 106x56mm. There's an optional "support" part which can be used to sandwich some fine aluminium mesh (or other filter material) between the two halves. You can also use the support as a template when cutting the mesh/filter.

These are pretty easy to fit with a 51mm / 2" hole saw and a jig saw.