Thanks for your replies. The links you folks provided were very helpful!
Well, it's like this; I'm trying to do something that neither Carl Zeiss or Tiffen intended (no big surprise here, right?) Here's the setup: Anniversary (I think) Speed Graphic and furnished with convertable Carl Zeiss Jena Tessar 4,5/150 T lens in a Synchro Compur shutter. The lens has a Tiffen #602 adaptor ring, Series 6 which seems to measure out to 43.5mm. The lens set up also has a Kodak Lens Hood Series 6, which when removed, the Tiffen retainer ring can mount to the Tiffen adaptor for drop-in Series VI filters.
Here's the Big Idea; which isn't working out too well yet. Apply a Cokin Series A adaptor ring to either the Tiffen adaptor ring, or the Kodak lens hood so I can use my collection of Cokin filters for B&W work. I have Cokin 52mm, 54mm and 55mm rings none of which fit the Kodak hood. I do not have smaller Cokin rings that might fit the Tiffen adaptor ring, and it seems like this isn't going to work with the whole Cokin theme.
So, barring that idea, I should probably find some Series VI filters and go from there.