Mamiya 645 Extention Tube 3 vs 3-S

I've been looking at getting a couple of extension tubes for my Mamiya 645 1000s and I know that there were at least four made:

#1
#2
#3
#3-s
And the Macro spacer for the 80mm f/4 macro lens.

What is the difference between the #3 and #3-S extension tubes?

Thanks!

...used tubes are usually very cheap for the M 645. They are fiddly to use. Just try comparing the working experience with that of a Nikon mount or Mamiya RB. Anyway, they are what they are. To answer your question, I believe the '3s' is the same size as the '3' but with the rear baffle slimmed down so vignetting is not cause with the 80mm f/1.9 lens. The 0.7m min focus on this lens is a real nuisance and the 45mm f/2.8 would be useful on a tube even thinner than any of those made. I'm considering a 80mm f/4 macro myself.