Usually, you can’t assume interchangeability just because two lenses look similar or share the same focal length and aperture. Manufacturers often change optical formulas, mounts, bevels, spacers, shims, and internal assemblies between versions—even within what seems like the same lens family.

The best clue is a service manual or parts list. If two parts have exactly the same part number, they’re much more likely to be the same. If the numbers differ, they should be treated as different parts. Even then, lens repair can require shims or alignment adjustments, so a matching-looking part may still not work correctly.

Optical elements are especially risky to swap. They may only be available as part of a grouped assembly, and small mechanical differences can prevent proper fit or calibration. In practice, only the manufacturer can definitively confirm compatibility.

So the safe rule is: assume lens elements are not interchangeable unless service documentation shows identical parts. Non-optical components such as autofocus motors, switches, or external hardware may have a better chance of being usable donor parts, but they still need matching part numbers or hands-on verification.