When to replace?
Hub liners can become loose, broken or worn causing annoying rocking and suprisingly severe damage to expensive component parts. Loose and broken liners are easily recognized. A worn hub liner will not be smooth on the inside where the threaded Post inserts into. Contrary to popular belief, the hub liner is not threaded! If it feels and looks like there are threads, replace it. Failure to do so will permit chair to be rocky.
Consider this professional rental tool which also easily installs hub liners
Otherwise, you will need to place something into the underside of the chair base that is 1" in diameter, and hammer it out. Be forewarned. You can spend a surprising amount of time and frustration in removing a simple plastic hub liner. Rent the tool and do the job in seconds.
Hub Liner #98 Installation
Style #98 hub liner has two characteristics to facilitate installation.
1. A small "notch" in the top surface of the collar portion.
2. A small raised squarish "bump" on the plastic tube about 5/8" down from the collar below the notch.
Also note that the metal tube into which the plastic hub liner inserts has either a notch or a stamped out hole. The "notch" on the top surface of the plastic Hub liner collar is to visually line up the "bump" with the space provided for in the metal tube.
As an alternative, you may consider cutting off and removing the raised "bump" with a sharp object., keeping the hub liner smooth. It fit's so tightly it is not going to move around anyhow.
Using a short piece of 2 x 4" about 3-4" long and a heavy hammer (16 oz.. and more), lay the 2 x 4" flat on the plastic collar and strike to get the hub liner started straight into the metal tube without any binding (cleaning may be necessary). When satisfied everything looks well, continue driving the plastic hub liner until it barely rests on top of the metal tube flange (a mating metal collar).