Is there a way to filter Belts by # of charm slots?

I can't find out anything about the code for the attribute so I'm guessing it doesn't exist, but on the chance I missed it, does anyone know how to specify the number of charm slots on a belt in a loot filter?

I'm trying to do a CharmSlots = 3 so I can highlight those, but no combination of Charm and/or Slots works.