These tow bars are used to connect the aircraft tractors, or tugs, to the aircraft. There is an eye at one end that attaches to the tractor and at the other is a set of adjustable claws that attach to the front wheel of the aircraft. The tractors previously towed aircraft with the tractor facing forwards, away from the aircraft, but in recent years that has changed to have the tractor facing towards the aircraft.
The pack has two tow bars in it. One is fully retracted for use with smaller aircraft or where there is no overhang of the nose of the aircraft. The other has one side of the tow bar extended out for use where there is an overhang of the aircraft's nose. The tow bar wheels can be positioned down when the tow bar is stored on the airfield, or being taken to an aircraft, or can be fixed raised up for use when towing.
The photos show one of the extended tow bars used to connect a Unimog tractor to a Harrier.