Flotsam,

The current series of Jobo tanks/drums were designed to be compatible with rotary processing in Jobo machines, while the previous series were not. While both generations of the smaller types are cross compatible, the larger types are not; the previous large type is actually smaller in diameter than the current one. So the spiral you have (which I think should be made out of transparent material for both spiral flanges) was for the previous larger series.

I acquired a few of these old large series spirals but without a tank to use them with, then another large format photographer friend bought a tank of this type with only one 4X5 rack; he was grinning ear to ear when I presented them with what I had. Best sort of a deal: I reclaimed some space, and he owes me one!