iirc the std type bush is a tight fit on the OD and is pinched on the metal insert that runs through the middle giving a torsional load, where the aftermarket types tend to be more of a bush, almost free floating.
This is why mine creaked as they were turning when the rear arm moved...
Lots of makes so this may be different by the brand.
One thing to remember is that injection moulded PU bushes set really badly and fatigue quite quickly due to the material properties required for volume moulding and ease of manufacture. For want of a better description cast bushes are best as the material is a different grade and will survive longer with a lot less setting and fatigue. They are harder to make so cost twice as much as most internet brands
