Info from Kevin Legacy April 2024:

Craig:  What you have provided is a complete list of the filters we offer for a Metrotom (when a filter changer is purchased).    Just so that you are aware, a “filter” in x-ray terms is a piece of metal (copper for instance) of a given thickness (0.5mm for instance).   There is nothing special about the metal or thickness.  I don’t know whom we procure from in Europe but all they do is buy sheet stock and cut to the right size (length and width) – approx.. ¾” x ¾”” to fit in the filter holder.   The filters are all the same size.  

For this reason, after receiving the initial set of filters from our factory (when we buy systems for a demo floor or lab) we just make our own filters as we need them = saves us money and allows us to make filters that might benefit the task at hand that are not available from ZEISS.  BTW – this is why one of the bullets below notes that there are “5 free slots” for customized filters.