Only flat, the head of plastic speaker stand (do not over tighten the mounting screws on the foot as the head too little break if you insist) metal would have been ideal but hey this is enough for the surround speakers.
As already mentioned, the mounting hardware provided for the enclosure only about those equipped with a "grommet" mounting. For others it is sufficient to adapt a screw at the right diameter, simple and effective but for those who do not have screws in stock with them, think about it before.