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Explanation: Here's a reference for both terms, although from a different industrial sector.
The belting (tappeto) stays on track (centered) on the belt conveyor.
Here's the example:
Each feeder belt has multiple ply rated belting. Rollers are 4"-5" diameter CEMA B/C. Feeder belts are to be driven by TEFC DC motors, with shaft mounted reducers. The head shaft pulley is self centering, herring bone lagged. The tail shaft wing pulley is self centering. Includes heavy duty head shaft and tail shaft bearings.
FYI: in your case you need a hyphen between "self" and "centering".