What are the differences between flat mount and post mount when it comes to bike disc brake caliper attachment?

Flat mount and post mount are two different types of mounting systems for attaching disc brake calipers to a bike frame.

Flat mount involves attaching the caliper directly to the frame or fork with two bolts, providing a sleek and low-profile look.

Post mount, on the other hand, uses two separate mounting points that are perpendicular to the frame or fork, allowing for more adjustability in caliper placement.

Overall, flat mount is becoming more common on modern road and gravel bikes, while post mount is still widely used on mountain bikes.