The "button" head is a keyed bolt, the stem has a slot in the hole that you cannot see when the bolt is in, that (is supposed to) keeps it from rotating when you tighten the nut.

The socket-head bolt likely has a shoulder on the inner face to prevent the nut from rotating. If it does, it doesn't; that is, it doesn't very well - I frequently see these with the shoulder damaged from the nut turning. Use a spanner.

And "aero"? Don't make me laugh, a human on a diamond frame bicycle is an aerodynamic disaster, the shape of the bar-clamp-bolt-head matters about as much as whether your mother had curly hair.