It is the defining failure of the product and it is decided at the factory, before anything is powder-coated.

What the pivot actually is

Every folding chair has a small number of pivots where the leg frames cross and where the seat links to them. Each one is a pin passing through two pieces of steel.

If that pin is a plain rivet through the tube wall, then the tube wall is the bearing. Steel rubbing on steel under load, a few hundred times, does what you would expect.

Why an oval hole cannot be fixed

Once the hole is oval, the geometry of the chair has changed. The leg frames no longer cross at the designed angle, so the four feet are no longer in one plane and the chair rocks on any floor.

Tightening it does nothing, because there is nothing to tighten — the material around the pin is gone. This is why wobbly folding chairs get scrapped rather than repaired.

What a shouldered pivot changes

A shouldered pivot has a machined bearing surface of the correct diameter, and it turns against a washer rather than against the frame. The wear happens on the washer, which is cheap, replaceable and doing its job.

It costs a small amount more per chair and it roughly triples the number of folds before the geometry starts to move.

What else to look at while you are there

Glides. A chair with bare tube ends will mark a floor and eventually cut into it; non-marking glides should be standard rather than an upgrade.

And the seat-to-frame fixings on resin chairs, which are where a UV-degraded shell cracks first. If the shell has gone chalky, check those before trusting the chair.