This hood fits to the existing bayonet attachment via a very tight friction fit. On first fitting it may feel you are forcing it, but this is normal and the mount has been tested across 3 different examples.
This is a small hood for the Voigtlander 35mm f1.4 Nokton Classic, Voigtlander 40mm f1.4 Nokton Classic lens or Zeiss 50mm f2 Planar lens as a replacement for the £48-70 ones from the OEMs. It gives that rectangular hood look, instead of the circular metal one.
It has been tested and is no problem on full frame as it's actually wider than it needs to be. It slightly intrudes into the viewfinder on a Leica M, which is why i'm offering a version with cutout as well if you need (see my other hoods).
This hood is mainly for the "look" - please see my other hoods for more compact, taylored hoods for these 3 lenses.