The bulge on the rear of a few FL lenses can interfere with the screw/lever on some adapters, on my Fotodiox FD adapter I just unscrewed the screw that engages the aperture lever and now there is no problem with those lenses. Canon FD lenses have an aperture lever that can be pushed to the end of its range and it stays there, this enables the aperture ring without having to use the lock ring on the adapter, only nFD lenses and perhaps 3rd party lenses will need the lock ring, just buy a second adapter if you need both.