Yup it's the nose grilles.
Version 1 is for the hybrid grilles, one end 2 section, one end 4 section
Version 2 is for the full set of 4 section
Version 3 is for the full set of 2 section
Note that although described as 37/4 detailing parts, they should actually be described as refurbished 37s as they are for all the subclasses /4 to /9.
37/4s were all refurbished early in the plan, so all of them had a full set of 4 section nose grilles when first converted.
Some grille swaps did happen, but I'm not aware of any 37/4s receiving 2 section grilles, doesn't mean it didn't happen though.