Jobo reels, 2501 vs 2502?

What is the difference?
I've got a whole bunch of reels here, some are clear plastic, some are black. Of the clear ones there are some shinier and clearer than others, although this may be just usage.
Some of the clear ones and all of the black ones have a little piece of plastic 1mm diameter 1cm long sticking out perpendicular at the end of the spiral.
All of them have space for the red clips (but only some have them, I presume the rest were lost).
All of them have the same length spirals to presumably take the same length of film.

According to the capacities, 2501 look like they can't take longer rolls of film. And I'm pretty sure that all of mine could take 2x 120s although I've never tried. Does that mean that they're all 2502s?

Here are a couple of photos of 2501 and 2502 reels. The one on the left is the 2501, it also needs a loader to work. Here is a video for the 2501: http://www.youtube.com/watch?v=1A10w1D8VmY. I have both clear and black 2502 reels, not really any difference in how they work. AFAIK both types will hold 2 rolls of 120, one 220 or one 35mm. I only use the red clips if I load 2 rolls of 120 on a single reel, otherwise I don't use them. The red clips are to keep the film from moving or sticking the the first film you load when you run 2 rolls of 120.