Yeah (and apologies if I get this wrong after 30 years) with a rolling airframe, you can have two fins on the same axis that "wiggle" back and forth at the same

Yeah (and apologies if I get this wrong after 30 years) with a rolling airframe, you can have two fins on the same axis that "wiggle" back and forth at the same frequency as the rotation of the missile. Direction control comes from the phase of the movement, so the fins are pushed in the direction you want to go when it rotates to that point.