The pictures of the actual mechanical Yaw Dampers that you see in your search results are off railway vehicles.
The mechanics of it are similar to a motor car shock absorber in that it is a cylinder and piston filled with oil. It is connected to the rail vehicle chassis/body at one end and the wheel bogie at the other end and prevents the bogie from "shimmying" at high speed.
In the UK, rail regulations stipulate that trains must have them fitted if they travel faster than 75mph.
Now back to aviation . . .