Esto dice la documentación de Flux sobre cómo agregar agujeros de montaje:

“Adding a Hole

In Flux, holes are a special type of pad. To create a hole, set a pad's Pad Type rule to HOLE.

This may sound strange, but it actually allows for a great deal of flexibility. You can move seamlessly between types without deleting anything. Start with a surface mount pad, then decide you need a through hole pad, or change the spec to a mounting hole, or add back an annular ring for better grounding.

Holes – also known as mounting holes, mechanical holes, or non-plated through-holes (NPTH) – serve a different function from vias. To connect a trace, polygon, or fill to another layer, use a via.

Flux currently only supports circular and pill shaped holes.

Adding a Net-connected Hole

You might want to add a hole that's connected to a net. For example, if you want to connect a mounting hole to ground. This is done in the same way as adding a pad with a couple extra steps:”