Heavy duty Gas Spring Pneumatic cylinder cartridge Spindle Strut Piston replacement for standard office chair. This cartridge Gas Spring has 4” Stroke Travel and is CLASS 4 with 400n. A standard cylinder is CLASS 3 with 300n (we do not sell class 3 cylinders). Main body is 1.1" (28mm) diameter and is 9.2” long. The tapered end that goes into the seat plate / mechanism has a standard 17-4 taper. The steel used is heat treated making it stronger. All hardware including bearing and retaining clip are included. CLASS 4 cylinders are typically installed on chairs up to 350 lb rating.