After first removing the 5 leg base from the gas cylinder, squirt a shot or two of WD-40 at the topside and underside of the column where it touches the 5 leg with caster wheel base. Sharply whack the side of the column 2-3 times setting up a vibration for the WD-40 to run down into the joint to facillitate removal.
Then, turn the base over and set 2-3 legs on a solid work surface for support. The base underside should now be facing upwards. With a STEEL hammer strike the thin protruding edge of the column with medium hard blows to drive it out (downward). Nine out of ten columns can be removed in this manner...sooner or later. If you have a Ten, you'll need to purchase a new gas cylinder with an included column. Most columns are easily removed. They are not welded in place.
If you purchased a new COM style gas cylinder (the column is included), remove the old column as described above. Next, remove the cylinder from the mechanism which is attached to the bottom of the chair seat using a pipe wrench or removal tool. To install the COM, shove the button end of the new cylinder up into the mechanism and other (column) end into the 5 leg base. That's all there is to it. Using the chair 2-3 times will tighten the press fit tapers to fit very tightly.
Commonly, columns today are 2" (50mm) diameter. much older chairs may be 1 3/4" (45mm). We have an limited stock of
1 3/4" (45mm) columns. Be sure to order a #108 bearing kit with schematic while ordering a column.
Do not be alarmed or concerned that the column extends below differently than the original and is not an exact match.