Refer to figures.
Construction of Oleo-pneumatic Struts

The outer cylinder is fixed rigidly to the airframe structure by two mounting brackets, and houses an inner cylinder and a piston assembly, the interior space being partially filled with hydraulic fluid and inflated with compressed gas (air or nitrogen). The inner cylinder is free to rotate and move up and down within the outer cylinder, but these movements are limited by the torque links, (scissor-links) which connect the inner cylinder to the steering collar. The steering collar arms are connected through spring struts to the rudder pedals, and a shimmy damper is attached to the steering collar.

Number 2 on the gear designates the movable inner cylinder.