Thanks for all the suggestions on identifying the NB filters in my newly-acquired wheel. To briefly recap, I bought some gear from an astronomer's widow, including a populated 7-slot 36mm ZWO EFW. No info was available re which filter was which. I identified LRGB by eye, and a series on the Ring Nebula (thanks Martin!) was definitive:
All three images were single frames, pulled into PixInsight with an identical HistogramTransformation applied (once) to each. Note the strong OIII, especially in the center, and the complete lack of response in one image, identifying the SII. Turns out the wheel was loaded LRGBSHO, perfectly sensible (these images are not presented in wheel order BTW).
Now comes another puzzle: What bandwidth are these filters? My friendly neighborhood spectroscopist offered to take them to work and scan 'em, but cautioned that he has to improvise to insert the filters in the machine, so results may not be definitive. Plus I'd have to pull everything apart and have the rig out of service for a few days.
I do have another imaging train with a set of 1.25" 7-nm, and one 3-nm Ha filter.
I could do something like shoot the Dumbbell with the known 7 and 3 H-alphas, as well as the unknown 36mm. (It would be a PITA to use the same camera on each wheel but not impossible.) The 7- and maybe 5-nm Ha image should include the NII known to be there, while a 3 should exclude it -- right?
What does the brain trust think? It's not as if my imaging will screech to a halt without this knowledge, but it is interesting to puzzle over. Spectroscopy is the obvious approach, but it would be fun to come up with something less direct.
