A missing clip lets a panel rattle, a stretched bolt loses its clamp load, and a corroded fastener seizes in the hole it was fitted to.
These parts are specified by thread, length, finish and, where relevant, by the built-in washer or the sealing patch on the thread. Fitting a hardware-store bolt in place of a factory fastener usually works until it does not: the wrong grade will not hold the torque the joint was designed for, and the wrong length will bottom out before it clamps.
Where a fastener is single-use by design — torque-to-yield head bolts, for example — it is listed as such and should not be reused.
