In a recent large acquisition, I got a bunch of film reels. I think they are Jobo reels for the 1500 tanks. They are white (or were, once upon a time) plastic, much like the Paterson reels only much thinner and with no ball bearings.
On the outside of one side of the reel is a red tab. When pushed in place, it sticks into the film path.
What is this for? Is it supposed to allow two rolls of film on one reel? And when would that be useful?
It is used for 2 rolls of film / 1 reel to keep them from overlapping.
It can also be used to force 1 roll on a reel to the outer part of the reel which is prefereable. If the roll moves inward during processing, it may not get enough processing solution coverage depending on how you process and how much chemistry you use.
At this point, I can't imagine wanting/needing to develop 6 rolls of film at once. But I think I'll hold on to them and see what the future brings. Who knows, some day I may get to take a vacation.