This is a twin-tube low pressure gas unit (similiar to most units that would be OE your vehicle).

The Monroe SensaTrac unit with PSD (position sensitive damping) and the Safe Tech" system combines exclusive precision tapered grooves in the pressure tube with application engineered valving and Fluon banded piston.

These features allow the Monroe Sensa-Trac strut to adjust more rapidly to changing road and weight conditions.

The tapered grooves are manufactured into the inside of the tube of the unit where the piston travels up and down, around the middle of total travel.