FWIW, those carriers - at least the one branded "Universal" - are designed to either be used with:
1) the glass installed, or
2) as a glassless carrier with the glass removed, in conjunction with a selection of various inserts with the size of each inserts being particular to a particular format.
I have one that I have modified slightly - thanks
@ozphoto - that allows me with glass installed to use it with a 6x9 negative, although my 7700s offer a light path that is right at its limits with that size. The modification does involve removing two of the four masking blades. I expect the modification is reversible.
GLWS.