Both photos above not same thing.
3” height Adjustable Chrome gas cylinder.
4 leg base polished metal 28” W diameter.
2” casters upgraded to bright metal, full hood, double wheel for all types of flooring.
Choose during checkout:
7" X 7" swivels only height adjustable seat plate with hole slots centered at each 5 1/2".
Or, swivel and rocker height adjustable seat mechanism SKU 3318G--6" X 10 1/4" hole slots on centers.
Square plate version: Floor to top of square plate with casters, 4 leg base, gas cylinder and square plate-Low is 14 3/4", high is 17 1/4".
Rock and Swivel 3318G version: Floor to top of mechanism with casters, base, gas cylinder, and swivel tilter mechanism-Low is 15 1/2", high is 18".
Simply insert without tools the gas cylinder into the center hole of the 4 leg chair base. Just sitting in the chair several times will make extremely tight and require tools to remove.
A mounting board may be necessary to install SKU 3318 or any other size mechanism.