Shimmy damper L O C K U N L O C K Piston Torque arm Fork Axle Lower locating cam Cylinder Upper locating cam Figure 13-22.  A towing lug on a landing gear is the designed means  for attaching a tow bar. Figure 13-20.  An upper locating cam mates into a lower cam recess  when the nose landing gear shock strut is extended before landing  and before the gear is retracted into the wheel well. Figure 13-21. A shimmy damper helps control oscillations of the  nose gear. Shock struts contain an instruction plate that gives directions  for filling the strut with fluid and for inflating the strut. The  instruction plate is usually attached near filler inlet and air  valve assembly. It specifies the correct type of hydraulic fluid  to use in the strut and the pressure to which the strut should be  inflated. It is of utmost importance to become familiar with  these instructions prior to filling a shock strut with hydraulic  fluid or inflating it with air or nitrogen.  towing or positioning the aircraft when on the ramp or in  a hangar. Disengagement of  this pin allows the wheel fork  spindle on some aircraft to rotate 360°, thus enabling the  aircraft to be turned in a tight radius. At no time should  the nose wheel of any aircraft be rotated beyond limit lines  marked on the airframe.  Nose and main gear shock struts on many aircraft are also  equipped with jacking points and towing lugs. Jacks should  always be placed under the prescribed points. When towing  lugs are provided, the towing bar should be attached only to  these lugs.  [Figure 13-22] 13-11