• Energy absorbing damper assembly for the arm rest.
• The LM had no seats, so the astronauts were restrained by cables attached to their space suits, and supported by their feet resting on the cabin floor, and by armrests.
• Two of these dampers were mounted on each arm rest to help absorb the inertia of the moving mass of the astronaut as the LM landed on the moon.

Also see:

Cutaway Grumman engineering drawing of the armrest damper: