Roland, what you call the matt black protectors around the rear lens element, I call rear stray light baffles, although I do acknowledge their dual role of helping to protect the rear lens elements of those lenses whose rear most lens elements are set well back into the camera body, e.g. fast primes of <85mm focal length. (Telephoto and micro Nikkors usually have their rear lens elements well inside the lens body.
No, what I am referring to is the wall thickness of the bayonet mount itself. For metal bayonet mounts, these mounts usually consist of hard chrome plated brass. Ideally the wall thickness of of the bayonet mount should be no more than 0.8mm where the contact block is screwed down. Lenses (typically most Ai and AiS and similar modern MF lenses) whose mounts have thick walls need the mount wall to be thinned down by carefully milling or filing the wall under where the contact block is fitted.
The attached image is a NOS mount from the 17-35mm AFS lens which has a wide 10-pin contact block fitted. Its mount has had its wall thickness reduced for the contact block as well in the region where the lens aperture lever is situated.