Do you happen to have any pictures of the nitecore diffuser on the zebralight?
I did take a couple of photos for you. However, I can't upload them here -- dragging-and-dropping failed, and linking to flickr didn't work either. Very frustrating. But I can assure you that the Nitecore NTW25 and and NDF25 fit well on my Zebralighit SC5w op. I've use them regularly outdoors to cross busy streets and indoors to read at night -- highly recommended.
However, as I mentioned above, the FastTech silicone diffuser is a difficult fit and I definitely do not recommend it for the SC5w.
In addition, I just received Olight TW10-O and TW10-W diffusers today. They
do not fit at all on my SC5. A couple of posts up, Overclocker shows one that fits nicely on his SC52. I guess the outer diameters of the SC5 and SC52 are different. In fact, I would say the outer diameters for these Olight diffusers is virtually the same as the outer diameter of my SC5 -- of course, in order for the diffuser to fit, the
inner diameter of the diffuser would have to match the outer diameter of the flashlight.